ArcGIS

9Using ArcGIS

Spatial Analyst
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DATA CREDITS
Quick-start tutorial data: courtesy of the state of Vermont
AUTHOR
Jill McCoy
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IN THIS CHAPTER
1
Using the Spatial Analyst tools available with ESRI
ArcGIS
, you can easily
perform spatial analysis on your data. You can provide answers to simple
spatial questions, such as How steep is it at this location? or What
direction is this location facing? Or you can find answers to more complex
spatial questions, such as Where is the best location for a new facility? or
What is the least costly path from A to B? The comprehensive set of
Spatial Analyst tools within ArcGIS allows you to explore and analyze your
spatial data and enables you to find solutions to your spatial problems. You
can run tools from the Spatial Analyst toolbox or the command line, accessible
via any ArcGIS Desktop application, or you can run tools from the
Spatial Analyst toolbar in ArcMap. You can also create your own custom
tools (models or scripts) to run a sequence of tools at one time.
Tutorial scenario
The town of Stowe, Vermont, USA, has experienced a substantial increase
in population. Demographic data suggests this increase has occurred due to
families with children moving to the region, taking advantage of the many
recreational facilities located nearby. It has been decided that a new school
must be built to take the strain off the existing schools, and as a town planner
you have been assigned the task of finding the potential site.
This tutorial will show you how to use many of the available tools and will
give you a solid basis from which you can start to think about how to solve
your own specific spatial problems.
Quick-start tutorial
* Exercise 1: Preparing for analysis
* Exercise 2: Finding a site for a
new school
* Exercise 3: Finding an alternate
access route to the new school
site
2 USING ARCGIS SPATIAL ANALYST
It is assumed that you have installed ArcGIS Desktop
(ArcView
, ArcEditor, or ArcInfo) and the Spatial
Analyst extension before you begin this tutorial. In
ArcGIS 8 versions, you accessed Spatial Analyst tools from
the Spatial Analyst toolbar in ArcMap. In ArcGIS 9, you
can still use the Spatial Analyst toolbar, but you can also run
tools from the SpatialAnalyst toolbox. Youll access tools in
the toolbox from the ArcCatalog tree or the
ArcToolboxwindow. The ArcToolbox window can be
docked in any ArcGIS Desktop application, meaning you
can run Spatial Analyst tools in applications such as
ArcCatalog, ArcScene, or ArcGlobe.
The data required is included on the ArcGIS Desktop CD.
After running the ArcGIS setup, on the Additional Installation
Components dialog box, check to install theArcGIS
Tutorial Data. In the ArcGIS Tutorial Data Setup wizard,
select to install the Spatial data (the default installation path
is C:\arcgis\ArcTutor\Spatial). The datasets were provided
courtesy of the state of Vermont for use in this tutorial. The
tutorial scenario is fictitious, and the original data has been
adapted for the purpose of the tutorial.
The datasets are:
Dataset Description
Elevation Raster dataset of the elevation of the
area
Landuse Raster dataset of the land use types
over the area
Roads Feature dataset displaying linear road
network for the town of Stowe
Rec_sites Feature dataset displaying point
locations of recreation sites
Schools Feature dataset displaying point
locations of existing schools
Destination Feature dataset displaying the
destination point used when finding
the best route for a new road
This tutorial is divided into exercises and is designed to let
you explore the SpatialAnalyst functionality in ArcGIS at
your own pace.
 In Exercise 1, youll prepare for analysis. Youll copy the
tutorial data locally and create a folder and a
geodatabase to hold your results. Youll learn the location
of the Spatial Analyst tools, create a hillshade
output, and explore your data.
 In Exercise 2, youll create a suitability map to help you
find the best location for a new school. You will derive
datasets of distance and slope, reclassify datasets to a
common scale, then weight those that are more important
to consider and combine them to find the most
suitable locations. Youll then locate the optimal site
using the selection tools within ArcMap.
 In Exercise 3, youll find the least costly route for an
alternate access road to the new school site.
You will need approximately 50 minutes of focused time to
complete the tutorial. Alternatively, you can perform the
exercises in sequence one at a time, saving your results
along the way when recommended.
QUICK-START TUTORIAL 3
Exercise 1: Preparing for analysis
In this exercise, youll prepare for analysis by first copying
the tutorial data locally, then creating a folder and a
geodatabase for your results. Youll locate the Spatial
Analyst tools and create a hillshade output to display
transparently with your other layers. Youll explore your
input data and open the ArcToolbox window. This exercise
will take approximately 15 minutes to complete.
Organizing your data
Before working with SpatialAnalyst tools, youll organize
your tutorial data using ArcCatalog.
Starting ArcCatalog
1. Start ArcCatalog by either double-clicking a shortcut
installed on your desktop or using the Programs list in
the Start menu.
Locating the tutorial data
By connecting to a folder in ArcCatalog, you can quickly
see the folders and data sources it contains. Youll now
begin organizing your tutorial data by establishing a folder
connection to its location.
1. Click the Connect to Folder button.
2. Type the pathname or navigate to the location where you
installed the tutorial data; for example, if you installed
ArcGIS on your C:\ drive, type
C:\arcgis\ArcTutor\Spatial, then click OK to establish
a folder connection.
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Your new folder connection to the tutorial data is listed in
the ArcCatalog tree.
Creating a working copy of the tutorial data
Youll now copy the tutorial data into a folder on a local disk
to maintain the integrity of the original data. Once it has
been copied, you will create a connection to the folder
containing the data.
1. Click the connection to the tutorial data (for example,
C:\arcgis\ArcTutor\Spatial), then click the Contents tab
and click the six datasets (schools.shp, roads.shp,
rec_sites.shp, destination.shp, landuse, and elevation)
contained within the folder.
Press and hold the Ctrl key while selecting the datasets
to select more than one.
2. Click the Copy button on the Standard toolbar.
3. Right-click the C:\ (or an alternative drive) folder
connection in the ArcCatalog tree, point to New, then
click Folder.
4. Rename the created folder Spatial, then press Enter.
5. Double-click the Spatial folder and click Paste on the
Standard toolbar to paste the copied datasets into it.
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QUICK-START TUTORIAL 5
6. Click the Connect to Folder button again, create a
connection to your Spatial folder, and click OK.
Your new folder connection, for example, C:\Spatial, is
now listed in the ArcCatalog tree, as shown in the
graphic that follows. You will access this connection
many times during this tutorial.
Creating a folder and a personal geodatabase for
results
In the next exercise, youll build a model that will help you
locate areas suitable for building a new school. Youll need
a folder to hold the majority of your results. Youll also need
a personal geodatabase to hold a feature class youll create.
By creating a feature class inside a geodatabase, youll be
able to use the default area field as part of the analysis.
Creating a new folder
Youll now create a Results folder. This folder will hold
results from your model in the next exercise.
1. Right-click the connection to your Spatial folder in the
ArcCatalog tree, point to New, and click Folder.
2. Type Results for the folder name and press Enter.
Creating a new personal geodatabase
Youll now create a Site.mdb geodatabase within the
Results folder. This geodatabase will hold results from your
model in the next exercise.
1. Right-click the Results folder, point to New, and click
Personal Geodatabase.
2. Right-click the personal geodatabase created and click
Rename.
3. Type Site and press Enter.
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Locating the Spatial Analyst tools
Spatial Analyst tools can be accessed via the Spatial
Analyst toolbar in ArcMap or via the Spatial Analyst Tools
toolbox. The toolbox is accessed via the Toolboxes folder in
the ArcCatalog tree or the ArcToolbox window.
The Toolboxes folder is not added to the ArcCatalog tree by
default. Youll add the Toolboxes folder so you can view the
Spatial Analyst tools that are available.
1. Click Tools on the Main menu and click Options.
2. Click the General tab and check Toolboxes if it is not
already checked.
3. Click OK on the Options dialog box.
4. Expand the Toolboxes folder, then expand the System
Toolboxes folder. Expand the Spatial Analyst Tools
toolbox to view the Spatial Analyst tools that are available.
They are organized into functional groups called
toolsets to make them easier to locate.
The ArcToolbox window can be used in any ArcGIS
Desktop application to access Spatial Analyst tools. Youll
learn more about the ArcToolbox window and also the
Spatial Analyst toolbar in this exercise.
5. Click File on the Main menu and click Exit to end the
ArcCatalog session.
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QUICK-START TUTORIAL 7
Starting ArcMap
1. Start ArcMap by either double-clicking a shortcut
installed on your desktop or using the Programs list in
the Start menu.
2. Click OK to open a new empty map.
Adding data to your ArcMap session
1. Click the Add Data button on the Standard toolbar.
2. Navigate to the folder on your local drive where you
copied the tutorial data (for example, C:\Spatial).
3. Click the destination dataset; press and hold down the
Shift key; then click elevation, landuse, rec_sites, roads,
and schools.
4. ClickAdd.
The datasets are added to the ArcMap table of contents
as layers.
Checking out a Spatial Analyst license
1. Click the Tools menu and click Extensions.
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2. Check Spatial Analyst.
3. Click Close.
Adding the Spatial Analyst toolbar
1. Click View on the Main menu, point to Toolbars and
click Spatial Analyst.
The Spatial Analyst toolbar is added to your ArcMap
session.
Creating a hillshade
Youll start out using the SpatialAnalyst toolbar. Youll run
the Hillshade tool so you can view and explore the output
from this tool with the rest of your input data later in this
exercise. A hillshade is a shaded relief raster created by
taking an elevation raster and setting an illumination source
(for example, the sun) at a user-specified azimuth (the
angular direction of the illumination source, in positive
degrees from 0 to 360) and altitude (the angle of the
illumination source above the horizon). The visual effect of
a hillshade can be dramatic when displayed transparently
over other layers in your ArcMap display.
1. Click the SpatialAnalyst dropdown arrow, point to
SurfaceAnalysis, and click Hillshade.
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2. Click the Input surface dropdown arrow and click
elevation.
3. Youll accept the default values set for the Azimuth and
Altitude parameters, since these values provide optimal
results when using a hillshade for display purposes.
4. Youll also accept the default and not model shadows, so
the local illumination of the surface will be calculated
whether or not a cell falls in the shadow of another cell.
If your x,y and z values are all in the same unit of measure
(for example, they are all in meters), you can accept the
default Z factor of 1, so the z units are not converted. The
x,y units in the elevation data, however, are in meters, and
the z values (the elevation values) are in feet. By multiplying
the z values by a z factor of 0.3048, they will be converted
to meters, since there are 0.3048 meters in one foot.
Note: Setting an appropriate z factor is critical for good
results if your input surface is stored in a geographic
coordinate system (for example, the x,y units are a spherical
measurement, such as decimal degrees or decimal
seconds). View the online Help for the Hillshade tool for an
explanation of suitable z factors.
5. Type a value of 0.3048 for the Z factor parameter.
6. The cell size (value of 30 meters) of the input dataset
will be used, as environment settings have not been
specified on the Options dialog box (accessed via the
Spatial Analyst toolbar context menu).
7. Instead of creating a temporary raster output, click in the
Output raster text box and remove the default text
<temporary>.
8. Type the pathname to your results folder (for example,
C:\Spatial\Results\) and type hillshd for the name of
the output.
A permanent result will be created.
9. Click OK to run the tool.
10. In the table of contents, click and drag the hillshade
result below landuse.
11. Check the elevation layer off.
Displaying and exploring data
You will now explore the display capabilities of ArcMap by
changing the symbology of one of the layers and applying
transparency so you can see the hillshade output you have
created underneath your other layers in the display.
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1. Right-click landuse in the table of contents and click
Properties.
2. Click the Symbology tab.
All landuse categories are currently drawn using cell values
as the Value Field and in random colors. You will change
the Value Field to be more meaningful and change the color
of each symbol to show a more appropriate color for each
landuse on the map.
3. Click the Value Field dropdown arrow and click
Landuse.
4. Double-click each symbol and choose a suitable color to
represent each landuse type (for example, water should
be blue).
5. Click OK.
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The changes you make are reflected in the table of
contents and in the map.
6. Click View on the Main menu, point to Toolbars, and
click Effects.
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7. Click the Layer dropdown arrow and click landuse.
8. Click the Adjust Transparency button and move the
slider to 30 percent transparency.
The hillshd layer can now be seen underneath the
landuse layer, giving a vivid impression of the terrain.
Highlighting a selection on the map
Examining the Attribute Table gives you an idea of the
number of cells of each attribute in the dataset.
1. Right-click landuse in the table of contents and click
Open Attribute Table.
Notice that Forest (value of 6) has the largest count,
followed by Agriculture (value of 5), then Water
(value of 2). The count is the number of cells in the
dataset with that value.
2. Click the row representing Wetlands (value of 7).
This selected set, all areas where the landuse is Wetlands,
is highlighted on the map.
3. Click the Options button on the Attributes of landuse
table, then click Clear Selection.
4. Click the Close button to close the Attributes of landuse
table.
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Identifying features on the map
1. Click the Identify tool on the Tools toolbar.
2. Click the Layers dropdown arrow on the Identify Results
dialog box and click <All layers>.
3. Click the Rec_site in the location shown to identify the
features in this particular location for all layers.
Note: Your display will not be zoomed in this much; this
is only to show the location of the recreation site to
click.
4. Expand each layer to obtain the value for each layer in
this location.
5. Close the Identify Results dialog box.
Examining a histogram
1. On the Spatial Analyst toolbar, click the Layer dropdown
arrow and click landuse.
2. Click the Histogram button.
The histogram displays the number of cells of each type
of landuse.
Since no cell size has been specified in the Cell Size tab
of the Options dialog box, the default takes the cell size
of the input25 meters in this case. If the cell size set
in the Options dialog box were larger, there would be
less cells of each landuse type, but each cell would
cover a larger area.
3. Close the histogram.
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QUICK-START TUTORIAL 13
Opening the ArcToolbox window
As well as accessing tools from the Spatial Analyst toolbar,
you can access similar tools and many more of them from
theArcToolbox window.
1. Click the Show/Hide ArcToolbox button on the Standard
toolbar of ArcMap to open the ArcToolbox window.
The window is placed within the application. Its position
may vary depending on the windows you have open.
From the ArcToolbox window, you can access all the
geoprocessing tools available with ArcGIS. There are more
than 450 tools available, including more than 150 Spatial
Analyst tools contained within the SpatialAnalyst Tools
toolbox. All tools can be run via dialog boxes or a command
line.
Docking the ArcToolbox window
The ArcToolbox window can be placed anywhere in the
application or on the desktop outside the ArcMap window.
1. Click and drag the bar at the top of the ArcToolbox
window.
2. Place the ArcToolbox window over the ArcMap table of
contents, then drop the panel. The outline of the
ArcToolbox window helps you place it in the desired
position.
Saving the map document
As the last step in this exercise, youll save the map document.
Youll use this map document in the next exercise.
1. Click File, then click Save As.
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2. Navigate to your Spatial folder and type
Site_Analysis.mxd for the filename.
3. Click Save.
In this exercise, you copied the tutorial data locally and
explored it, learned how to access Spatial Analyst tools, and
learned how to run them from the Spatial Analyst toolbar.
In the next exercise, youll build a model by adding tools
from the Spatial Analyst Tools toolbox to a ModelBuilder
window to run a sequence of tools that will locate the areas
that are suitable for building a new school.
You can continue on to Exercise 2 or stop and complete the
tutorial at a later time. If you do not move on to Exercise 2
now, do not delete your working copy of the tutorial data or
the folder connection that accesses it in ArcCatalog.
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QUICK-START TUTORIAL 15
Exercise 2: Finding a site for a new school in Stowe, Vermont
In this exercise, you will build a model that finds suitable
locations for a new school. The steps to produce such a
suitability map are outlined below.
Your input datasets in this exercise are landuse, elevation,
rec_sites, and schools. You will derive slope, distance to
recreation sites, and distance to existing schools, then
reclassify these derived datasets to a common scale from
110. You will then weight them according to a percentage
influence and combine them with landuse data to produce a
map displaying suitable locations for the new school. Youll
then select the optimal site for the new school from the
alternatives.
This exercise will take approximately 20 minutes to com-
plete.
Setting up
If you are continuing on from the previous exercise and
have the Site Analysis map document open, skip the next
three steps and go to the next section, Creating a new
toolbox.
1. Start ArcMap by either double-clicking a shortcut
installed on your desktop or using the Programs list in
the Start menu.
2. Click C:\Spatial\Site Analysis.mxd in the Browse for
maps list to open the map document created in the
previous exercise.
3. Click the Show/Hide ArcToolbox button on the Standard
toolbar to open the ArcToolbox window if it is not
present.
Creating a new toolbox
Youll first create a new toolbox to hold the models you will
create in this exercise and the next one.
The default location for new toolboxes created in the
ArcToolbox window is generally \Documents and
Settings\yourlogin\Application Data\ESRI\ArcToolbox\My
Toolboxes. Youll change this path to be your
Spatial\Results folder.
1. Click Tools on the Main Menu and click Options.
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2. Click the Geoprocessing tab.
3. Type C:\Spatial\Results (or an alternative drive) for
the location of the My Toolboxes folder.
4. Click OK.
All toolboxes created in the ArcToolbox window within
ArcMap will be created in this location.
5. Right-click the ArcToolbox window and click New
Toolbox.
6. Change the default name for the toolbox to Site Analysis
Tools, then click Enter.
7. Right-click the SiteAnalysis Tools toolbox and click
Properties.
8. Check that the location of the toolbox on disk is your
Results folder.
9. Click OK.
Creating a new model
You can perform your Spatial Analyst tasks by simply
opening tool dialog boxes, supplying values for parameters,
and clicking OK to run each tool, one after another. Alternatively,
you can run tools at a command line. For information
on running tools at the command line, see Chapter 7 of
Geoprocessing in ArcGIS. If you intend to run a sequence
of tools, experiment with parameter values to achieve the
desired result, or package your methodology so others can
apply it to their data, you should build a model. A model is
built by stringing tools together inside a ModelBuilder
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window. Once your model is created, you can easily
experiment with parameter values, use different input data,
run the model over and over again, and share it with others.
In this exercise, you will create a model to find a suitable
location for a new school.
1. Right-click the Site Analysis Tools toolbox, point to New,
and click Model.
An empty ModelBuilder window will open.
Renaming the model
1. Click the Model menu and click Model Properties.
2. Click the General tab.
3. Type find_site in the Name text box and Find location
for school in the Label text box. The name is used in
scripting and at the command line. The label is the
display name for the model.
4. Check Store relative path names so that all paths for
sources of information referenced by the tool are saved
relative to the location of the toolbox. If the toolbox and
its data are moved, paths to data sources will be altered
accordingly.
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Specifying environment settings
Before you start to perform analysis on your data, you
should set up any relevant environment settings.
When running tools via the SpatialAnalyst toolbar, youll set
environment settings in the Options dialog box (accessed
via the Spatial Analyst toolbars context menu). When
working with tools via the SpatialAnalyst Tools toolbox,
youll set environment settings via the Environment Settings
dialog box. Although they have similar properties, the
SpatialAnalyst toolbox Options environment settings and
the ArcToolbox environment settings do not share information
or interact.
There are three levels at which you can set environment
settings when working with tools in the SpatialAnalyst
Tools toolbox. You can specify environment settings for the
application that will apply to all tools (right-click the
ArcToolbox window and click Environments to access the
Environment Settings dialog box).Alternatively, you can set
environment settings for a specific model or for a process
within a model (right-click the tool element of a process in a
model and click Properties to override environment settings
for a model or the application). Environment settings for the
application are used by default unless they are specified for
a model or for a process within a model. Settings for a
model will override settings for the application. Settings for
a process will override settings for the application and the
model to which the process belongs. For more information
on environment settings, see Chapter 6 of Geoprocessing
in ArcGIS.
As your environment settings apply to each process of this
model only, youll set environment settings for the model.
1. Click the Environments tab.
2. Expand the General Settings tree.
3. Check Current Workspace, Output Extent, and Scratch
Workspace.
4. Expand the Raster Analysis Settings tree.
5. Check Cell Size.
6. Click Values.
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7. Expand the General Settings section.
8. In the Current Workspace text box, type the pathname to
your Spatial folderfor example, C:\Spatialfor its
value. Alternatively, click the Browse button to the right
of the Current Workspace text box and navigate to this
location. The Current Workspace is the location of your
project data.
9. In the Scratch Workspace text box, type the pathname to
your Results folderfor example,
C:\Spatial\Resultsfor its value.Alternatively, click
the Browse button to the right of the Scratch Workspace
text box and navigate to this location. The Scratch
Workspace will be set by default as the path for outputs
from running tools.
Youll also set the extent for results from running Spatial
Analyst tools to be the same as the elevation data, as this is
the approximate boundary of your study area. All results
generated will have the same extent as the elevation
dataset.
10. Click the Output Extent dropdown arrow and click
Same as Layer elevation.
11. Expand the Raster Analysis Settings section.
12. Your elevation dataset has the largest cell size (30
meters). Click the Cell Size dropdown arrow and click
Same as Layer elevation. The cell size of your
elevation layer will be applied to all subsequent raster
outputs.
Note: Setting a smaller cell size than your largest input
will not mean you have more detailed information in
subsequent raster results; you will just have more cells
of the same value which may affect your display and
calculation speeds. Although the software does not
prevent it, it is considered incorrect to set a cell size
smaller than your largest input cell size.
13. Click OK on the Environment Settings dialog box.
14. Click OK on the Model Properties dialog box.
15. Click the Model menu and click Save.
The models properties are updated.
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Deriving datasets
In the previous exercise, you added the input datasets that
you will use in the model to your ArcMap session. Youve
set up environment settings. You are ready to start to
process your project data to locate suitable areas for the
new school. Youll derive the following from your project
data:
 Slope from elevation
 Distance from recreation sites
 Distance from existing schools
Deriving slope
Since the area is mountainous, you need to find areas of
relatively flat land to build on, so you will take into consideration
the slope of the land.
1. In the Spatial Analyst Tools toolbox, expand the Surface
toolset.
2. Click and drag the Slope tool into the ModelBuilder
window.
An element that references the Slope tool is created in
the display window.
3. Right-click the Slope tool element and click Open.
4. Click the Input raster dropdown arrow and click the
elevation layer. Note that layers are denoted with a
yellow icon in the dropdown list.
5. Accept the default path and name given for the Output
raster parameter value. The default path is set to the
scratch workspace you set up earlier in the Environment
Settings dialog box.
6. Leave the default for the Output measurement parameter
to calculate slope in degrees.
7. As you did when calculating hillshade, type 0.3048 for
the value of the Z factor parameter to convert the z
values to the same unit of measure as the x,y units (from
feet to meters).
8. Click OK.
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9. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
Notice that the process is now colored in, meaning it is
ready to run.
10. Right-click the derived data element for the Slope tool
and click Rename.
11. Type Slope output and click OK.
Note: Renaming an element label does not alter the
name of the output on disk.
12. Right-click the Slope output data element again and
click Add To Display.
With the Add To Display property checked, the derived
data referenced by this element will be added to the
display each time the model is run from the
ModelBuilder window.
13. Right-click the Slope tool element and click Run.
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Notice that as the tool of the process runs, its progress
is documented in the progress dialog box and the tool
element that references the tool is highlighted in red.
When the tool has finished running, the tool element and
its derived data element become shaded, indicating that
it has run and the derived data has been created on
disk.
14. Check the Close this dialog when completed successfully
check box if the Slope progress dialog box is
present, then click Close.
15. Examine the layer added to your ArcMap display. Steep
slopes are displayed in red, less steep slopes in green in
the output layer.
Deriving distance from recreation sites
To find locations close to recreation sites, you must first
calculate the Euclidean (straight-line) distance from recreation
sites.
1. In the Spatial Analyst Tools toolbox, expand the Distance
toolset.
2. Click and drag the Euclidean Distance tool into the
ModelBuilder window.
An element that references the Euclidean Distance tool
is created in the display window.
3. Right-click the Euclidean Distance tool element and click
Open.
4. Click the Input raster or feature source data dropdown
arrow and click the rec_sites layer.
5. Accept the default path for the value of the Output
distance raster parameter, but type EucD_rsites for
the name.
Instead of specifying a set distance from each point to
use when calculating the output, youll accept the default
value for the Maximum distance parameterthe edge
of the output raster is used as the maximum distance.
The cell size is taken from the environment setting that
you set up previously to be the same as your elevation
data. In this exercise, the Output direction raster is not
required.
6. Click OK.
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7. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
8. Right-click the EucD_rsites derived data element for the
Euclidean Distance tool and click Rename.
9. Type Distance to recreation sites in the Enter new
element name text box and click OK on the Rename
dialog box.
10. Right-click the Distance to recreation sites derived data
element and click Add To Display.
11. Right-click the Euclidean Distance tool element and
click Run to run the process.
12. Examine the layer added to your ArcMap display.
Distances increase the farther you are from a recreation
site.
Deriving distance from schools
To find locations away from existing schools, you must first
calculate the Euclidean (straight-line) distance from
schools.
1. In the Spatial Analyst Tools toolbox, expand the Distance
toolset.
2. Click and drag the Euclidean Distance tool into the
ModelBuilder window.
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An element that references the Euclidean Distance tool
is created in the display window.
3. Right-click the Euclidean Distance (2) tool element and
click Open.
4. Click the Input raster or feature source data dropdown
arrow and click the schools layer.
5. Accept the default path for the value of the Output
distance raster parameter, but type EucD_sch for the
name.
As with the distance to rec_sites output, instead of specifying
a set distance from each point to use when calculating
the output, youll accept the default value for the Maximum
distance parameterthe edge of the output raster is used
as the maximum distance. The cell size is taken from the
environment setting that you set up previously to be the
same as your elevation data. In this exercise, the Output
direction raster is not required.
6. Click OK.
7. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
8. Right-click the derived data element for the Euclidean
Distance tool and click Rename.
9. Type Distance to schools and click OK.
10. Right-click the Distance to schools derived data element
and click Add To Display.
11. Right-click the Euclidean Distance (2) tool element and
click Run to run the process.
12. Examine the layer added to your ArcMap display.
Distances increase the farther you are from a school.
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Reclassifying datasets
After deriving the necessary datasets, you are ready to
combine them to locate suitable sites for the new school. It
is not possible to combine the datasets you have derived
and landuse in their present formfor example, combining
a cell value in which slope equals 15 degrees with a cell
value in which distance to schools equals 5 miles and one in
which the cell value for landuse equals 7 (forest)and get
a meaningful answer that you can compare to other locations.
To combine the datasets, they need to be set to a
common measurement scale. That common measurement
scale is what determines how suitable a particular locationeach
cellis for building a new school.
Using the Weighted Overlay dialog box, you can weight the
values of each dataset, then combine them at one time.
However, the inputs for the Weighted Overlay tool must
contain discrete, integer values. Landuse is already categorized
into discrete values; for example, forest equals a value
of 7, so you can simply add this dataset directly into the
Weighted Overlay dialog box and assign weights to the
input cell values. The values in the datasets you derived in
previous steps are all floating point, continuous datasets,
categorized into ranges, and they must first be reclassified
so that each range of values is assigned one discrete,
integer value. Potentially, the value given to each range can
be any value, provided you note the range that the value
corresponds to. This is because you can weight these
values within the Weighted Overlay dialog boxthe next
step after reclassifying the derived datasets. However, it is
easier to weight the cell values for derived datasets while
reclassifying. In the Weighted Overlay dialog box, you can
accept the default and leave the scale values the same as
the input values.
You will reclassify each derived dataset to a common
measurement scale, giving each range a discrete, integer
value between 1 and 10. Higher values will be given to
attributes within each dataset that are more suitable for
locating the school.
Reclassifying slope
It is preferable that the new school site be located on
relatively flat ground. Youll reclassify the slope output,
slicing the values into equal intervals. Youll give a value of
10 to the most suitable range of slopesthose with the
lowest angle of slopeand 1 to the least suitable range of
slopesthose with the steepest angle of slopeand rank
the values in between linearly.
1. In the Spatial Analyst Tools toolbox, expand the Reclass
toolset.
2. Click and drag the Reclassify tool into the ModelBuilder
window.
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An element that references the Reclassify tool is
created in the display window.
3. Right-click the Reclassify tool element and click Open.
4. Click the Input raster dropdown arrow and click the
variable Slope output. Variables are denoted with blue
icons in the dropdown list. When you drag data into a
ModelBuilder window or set the data referenced by
input or derived data elements within a tools dialog box,
the elements created in the ModelBuilder window are
variables that can be shared between processes.
5. Accept the default for the Reclass field parameter so
the Value field will be used.
6. Click Classify.
7. Click the Method dropdown arrow and click Equal
Interval.
8. Click the Classes dropdown arrow and click 10.
9. Click OK.
You want to reclassify the slope layer so steep slopes are
given low values, since these are least suitable for building.
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15. Type Reclassed slope in the Enter new element name
text box and click OK.
16. Right-click the Reclassed slope derived data element
and click Add To Display.
17. Right-click the Reclassify tool element and click Run to
run the process.
18. Examine the layer added to your ArcMap display.
Locations with higher valuesless steep slopesare
more suitable than locations with lower valuessteeper
slopes.
10. Click Reverse New Values so that ranges of values
representing less steep slopes receive a higher new
value, since these areas are more suitable for building.
11. Accept the default path for the value of the Output
raster parameter, but type Rslope for the name.
12. Click OK.
13. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
14. Right-click the derived data element for the Reclassify
tool and click Rename.
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Reclassifying distance to recreation sites
The school should be located as close as possible to a
recreational facility. You will reclassify the distance to
recreation sites output, giving a value of 10 to ranges of
values that represent areas closest to recreation sitesthe
most suitable locationsgiving a value of 1 to ranges of
values that represent areas far from recreation sitesthe
least suitable locationsand ranking the values linearly in
between.
1. In the Spatial Analyst Tools toolbox, expand the Reclass
toolset.
2. Click and drag the Reclassify tool into the ModelBuilder
window.
An element that references the Reclassify tool is
created in the display window.
3. Right-click the Reclassify (2) tool element and click
Open.
4. To connect the output from the Euclidean Distance tool
as input for the Reclassify (2) tool, click the Input raster
dropdown arrow and click the variable Distance to
recreation sites.
5. Accept the default for the Reclass field parameter so
the Value field will be used.
6. Click Classify.
7. Click the Method dropdown arrow and click Equal
Interval.
8. Click the Classes dropdown arrow and click 10.
9. Click OK.
You want the school to be close to a recreational facility, so
you will give higher values to ranges of values that represent
locations close to recreational facilities, since distances
that are close are most desirable.
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10. Click Reverse New Values so that distances close to
recreational facilities receive a higher new value, since
these areas are more desirable.
11. Accept the default path for the value of the Output
raster parameter but change the default name to
Rdist_rec.
12. Click OK.
13. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
14. Right-click the derived data element for the Reclassify
(2) tool and click Rename.
15. Type Reclassed distance to recreation sites and click
OK.
16. Click the Reclassed distance to recreation sites derived
data element, move the cursor over one of the blue
handles surrounding the element, then click and drag to
resize the element so all text can be seen.
17. Right-click the Reclassed distance to recreation sites
derived data element and click Add To Display.
18. Right-click the Reclassify (2) tool element and click Run
to run the process.
19. Examine the layer added to your ArcMap display.
Locations with higher valuesareas close to recreation
sitesare more suitable than locations with lower
valuesareas far from recreation sites.
Reclassifying distance to schools
It is necessary to locate the new school away from existing
schools to avoid encroaching on their catchment areas. You
will reclassify the Distance to schools layer, giving a value
of 10 to areas farthest from existing schoolsthe most
suitable locationsgiving a value of 1 to areas near existing
schoolsthe least suitable locationsand ranking the
values in between linearly. By doing this, you will find out
which areas are near and which areas are far from existing
schools.
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1. In the Spatial Analyst Tools toolbox, expand the Reclass
toolset.
2. Click and drag the Reclassify tool into the ModelBuilder
window.
An element that references the Reclassify tool is
created in the display window.
3. Right-click the Reclassify (3) tool element and click
Open.
4. Click the Input raster dropdown arrow and click the
Distance to schools variable.
5. Accept the default for the Reclass field parameter so
the Value field will be used.
6. Click Classify.
7. Click the Method dropdown arrow and click Equal
Interval.
8. Click the Classes dropdown arrow and click 10.
9. Click OK.
You want to position the school away from existing schools,
so you will give higher values to ranges of values that
represent locations farther away, as these locations are
most desirable. As the default gives high New values
more suitable locationsto high ranges of Old values
locations farther away from existing schoolsyou do not
need to change any values this time.
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10. Accept the default path for the value of the Output
raster parameter, but type Rdist_sch for the name.
11. Click OK.
12. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
13. Right-click the derived data element for the Reclassify
(3) tool and click Rename.
14. Type Reclassed distance to schools and click OK.
15. Right-click the Reclassed distance to schools derived
data element and click Add To Display.
16. Right-click the Reclassify (3) tool element and click Run
to run the process.
17. Examine the layer added to your ArcMap display.
Locations with higher valuesareas away from existing
schoolsare more suitable than locations with lower
valuesareas close to existing schools.
18. Click the Model menu and click Save.
Weighting and combining datasets
You are now ready to combine the derived datasets and
landuse to find the most suitable locations. The values of
the derived datasets representing slope, distance to recreation
sites, and distance to schools have all been reclassified
to a common measurement scale (more suitable cells have
higher values). The landuse dataset is still in its original
form because you can weight the cell values for this dataset
as part of the weighted overlay process. Values representing
areas of water and wetlands will be restricted. Youll
also mark slope values that are less than 4 (the least
suitable because they are too steep) as restricted so these
values can be excluded. Youll learn more about restricted
values and NoData later in this exercise. If all datasets
were equally important, you could simply combine them,
giving each equal influence; however, you have been
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informed that it is preferable to locate the new school close
to recreational facilities and away from other schools. You
will weight all the inputs, giving each a percentage of
influence. The higher the percentage, the more influence a
particular input will have in the suitability model.
You will give the inputs the following percentages of
influence:
Reclassed distance to rec_sites: 50%
Reclassed distance to schools: 25%
Reclassed slope: 13%
Landuse: 12%
1. In the Spatial Analyst Tools toolbox, expand the Overlay
toolset.
2. Click and drag the Weighted Overlay tool into the
ModelBuilder window.
An element that references the Weighted Overlay tool is
created in the display window.
3. Right-click the Weighted Overlay tool element and click
Open.
The default evaluation scale is from 1 to 9 by 1. A scale of
110 was used when reclassifying datasets, so before
adding input rasters to the Overlay tool, youll set the
evaluation scale from 1 to 10 by 1. This means you will
avoid having to update the scale values after adding your
input datasets.
4. Type 1, 10, and 1 in the From, To, and By text
boxes.
5. Click the Add Raster Row button to add the input
rasters.
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6. Click the Input raster dropdown arrow and click the
Reclassed distance to schools variable.
7. Accept the default Input field and click OK.
The raster is added to the Weighted Overlay dialog box.
The Field column displays the values of the Reclassed
distance to schools output. The Scale Value column
mimics the Field column because the evaluation scale
was set to encompass the range of values in each input
raster. You could modify the scale values for each class
at this point, but for this input, the values were already
weighted appropriately at the time of reclassifying.
8. Click the Add Raster Row button again to add the next
input raster.
9. Click the Input raster dropdown arrow and click the
Reclassed distance to recreation sites variable.
10. Accept the default value for the Input field parameter
and click OK.
The raster is added to the Weighted Overlay dialog box.
The Field column displays the values of the Reclassed
distance to recreation sites output. As with the
Reclassed distance to schools input, the Scale Value
column mimics the Field column because the evaluation
scale was set to encompass the range of values in each
input raster. You could modify the scale values for each
class at this point, but again, for this input, the values
were already weighted appropriately at the time of
reclassifying.
11. Click the Add Raster Row button again to add the next
input raster.
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12. Click the Input raster dropdown arrow and click the
Reclassed slope variable.
13. Accept the default value for the Input field parameter
and click OK.
The raster is added to the Weighted Overlay dialog box.
14. Scroll down to the Reclassed slope input.
Again, for this input, the values were already weighted
appropriately at the time of reclassifying. However, you
know you definitely do not want to build on slopes greater
than about 35 percent, even if all other conditions are
perfect. Youll make values from 1 to 3 restrictedsince
these values represent slopes from 37.17263985
53.1037712 (the maximum slope).
Setting a scale value to restricted assigns a value to that cell
in the output weighted overlay result that is the minimum
value of the evaluation scale set minus one (zero in this
exercise). If there are no inputs to the Weighted Overlay
dialog box with cells of NoData, you could use NoData as
the scale value to exclude certain values. However, if you
have NoData cells in any of your inputs, it is safest and
essential to use Restricted instead. Potentially, you could
have a result from the Weighted Overlay dialog box that
contains cells of NoData that have come from one or more
of the inputs (NoData on any input equals NoData in the
result) and Restricted areas that you intentionally excluded.
NoData and Restricted values should not be confused.
Each serves a specific purpose. There may be areas of
NoData where you dont know the value but that are
actually suitable areas. If you use NoData to exclude
certain cell values and there is NoData in one or more
inputs, you will not know whether a cell of NoData means
the area is restricted from use or there was no input data
available in that location.
15. In the Scale Value column for the Reclassed slope
raster, click the cell with a value of 1.
16. Click the dropdown arrow and click Restricted.
17. Follow this procedure for scale values of 2 and 3.
18. Click the Add Raster Row button again to add the last
input raster.
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19. Click the Input raster dropdown arrow and click the
landuse layer.
20. Click the Input field dropdown arrow and click Landuse.
21. Click OK.
All input rasters are now added to the Weighted Overlay
dialog box.
22. Scroll down to the landuse input.
Youll now weight the scale values of the landuse layer so
they are comparable with the other inputs. A lower value
indicates that a particular landuse type is less suitable for
building. The scale values for Water and Wetlands will be
set as Restricted, since they cannot be built on and should
be excluded.
23. Change the default scale values for the landuse layer to
the following values:
Brush/transitional5
Barren land10
Built up3
Agriculture9
Forest4
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Youll now set the scale values representing Water and
Wetlands to Restricted.
24. In the Scale Value column, click the cell next to the
landuse type Water.
25. Click the dropdown arrow and click Restricted.
26. In the Scale Value column, click the cell next to the
landuse type Wetlands.
27. Click the dropdown arrow and click Restricted.
28. Collapse each raster in the Weighted overlay table.
Youll now assign a percentage of influence to each raster,
based on how much importance (or weight) each should
have in the final suitability map.
29. In the % Influence column, type the following percentages
for each of the input rasters:
Reclassed distance to schools 25
Reclassed distance to recreation sites 50
Reclassed slope 13
landuse 12
30. Accept the default path for the Output raster parameter
value, but type suit_areas for the name.
31. Click OK.
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36. Right-click the Weighted Overlay tool element and click
Run to run the process.
37. Examine the layer added to your ArcMap display.
Locations with higher values indicate more suitable
sitesareas that are on less steep slopes of suitable
landuse types, closer to recreational facilities, and away
from existing schools.
Selecting optimal sites
Youll use a conditional expression in the Con tool to extract
only the optimal sites. It has been decided that those sites
that are considered optimal must have a suitability value of
9 (the highest value in the suit_areas output). In the conditional
expression, all areas with a value of 9 will retain their
original value (9). Areas with a value of less than 9 will be
changed to NoData.
32. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
33. Right-click the derived data element for the Weighted
Overlay tool and click Rename.
34. Type Suitable Areas and click OK.
35. Right-click the Suitable Areas derived data element and
click Add To Display.
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1. In the SpatialAnalyst Tools toolbox, expand the Conditional
toolset.
2. Click the Con tool and drag it into the ModelBuilder
window.
An element that references the Con tool is created in the
display window.
3. Right-click the Con tool element and click Open.
4. Click the Input conditional raster dropdown arrow and
click the Suitable Areas variable.
5. Click the Input true raster or constant value dropdown
arrow and, again, click the Suitable Areas variable.
If the condition youll enter is true of the cells in the
Input conditional raster, the value of the cells of the
Input true raster or constant value will be applied to the
cells of the output raster.
6. Leave the value for the Input false raster or constant
value parameter blank. The default will be appliedany
value in the Input conditional raster that doesnt meet
the condition youll enter will be given NoData in the
output raster.
7. Accept the default path for the Output raster parameter
value, but change the default name to opt_areas.
8. Type Value = 9 for the value of the Expression
parameter.
If a cell value in the conditional raster (Suitable Areas) is
9, it will retain its original value (of 9) in the result. If a
cell value is not 9, it will be given NoData. This way, you
will exclude all areas but those most suitable for locating
the school.
9. Click OK.
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10. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
11. Right-click the derived data element for the Con tool
and click Rename.
12. Type Output optimal areas raster in the Enter new
element name text box and click OK on the Rename
dialog box.
13. Right-click the Output optimal areas raster derived data
element and click Add To Display.
14. Right-click the Con tool element and click Run to run
the process.
15. Examine the layer added to your ArcMap display. These
are the optimal locations for siting the new school.
There are many single cells representing optimal
locations. These 30 meter cells are too small for the
school site. Youll clean up the result, removing these
small areas, using the Majority Filter tool.
16. In the Spatial Analyst Tools toolbox, expand the Generalize
toolset.
17. Click the Majority Filter tool and drag it into the
ModelBuilder window.
An element that references the Majority Filter tool is
created in the display window.
18. Right-click the Majority Filter tool element and click
Open.
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19. Click the Input raster dropdown arrow and click the
Output optimal areas raster variable.
20. Accept the default path for the value of the Output
raster parameter, but change the name for the output
raster to opt_areasM.
21. Click the Number of neighbors to use dropdown arrow
and click EIGHT.
This option specifies the number of neighboring cells to
use in the kernel of the filter. The kernel of the filter will
be the eight nearest neighbors (a 3-by-3 cell window) to
the present cell.
22. Accept the default to use the MAJORITY as the
replacement threshold. Five out of eight connected cells
must have the same value for the present cell to retain
its value.
23. Click OK.
24. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
25. Right-click the derived data element for the Majority
Filter tool and click Rename.
26. Type Output filtered optimal areas raster and click
OK.
27. Right-click the Output filtered optimal areas raster
derived data element and click Add To Display.
28. Right-click the Majority Filter tool element and click
Run to run the process.
29. Examine the layer added to your ArcMap display.
Compare it to the layer opt_areas. Many optimal areas
that were considered too small in area have been
removed.
Note: If you want to remove areas of multiple cells, you
would use the Nibble tool.
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Setting model parameters
After completing your model, you can set variables as
model parameters so they will display on the dialog box of
your model. If you plan to distribute your model, you should
set model parameters so the users of your model can
specify the input parameters. In the case of this suitability
model, it could be applied to a different area, using different
input data, for instance.
First, youll rename the input data variables and the final
output variable, for these names will become the parameter
labels in the models dialog box.
1. Right-click the landuse project data element and click
Rename.
2. Type Input landuse raster and click OK.
3. Right-click the elevation project data element and click
Rename.
4. Type Input elevation raster and click OK.
5. Right-click the rec_sites project data element and click
Rename.
6. Type Input recreation sites feature class and click
OK.
7. Right-click the schools project data element and click
Rename.
8. Type Input schools feature class and click OK.
9. Right-click Input landuse raster, Input elevation raster,
Input schools feature class, and Input recreation sites
feature class and click Model Parameter.
10. Right-click the Output filtered optimal areas raster
derived data element and click Model Parameter.
11. Click the Model menu and click Save, then click the
Model menu again and click Close.
Viewing the modeľs dialog box
1. Right-click the Find location for school model in the
ArcToolbox window and click Open.
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The variables you made into model parameters are displayed
as the parameters on the models dialog box. Users
of your model can simply enter their own parameter values
to find suitable locations for a school in their area without
having to know much information about the underlying
workings of the model. They would, of course, have to have
the same fields present in the landuse data, understand the
methodology of the model, and agree with the assumptions
applied. This information can be documented with the tool.
Note: a dataset called opt_areasM already exists as you
have previously created it. This output cannot be overwritten
by default. To change the default behavior so results
can be overwritten, click Tools on the Main menu and click
Options. Click the Geoprocessing tab and check Overwrite
the outputs of geoprocessing operations.
2. Click Cancel on the models dialog box.
The Documentation Editor can be used to add documentation
to your tools.
3. Right-click the model and click Edit Documentation.
For more information on documenting your tools, see
Chapter 5 of Geoprocessing in ArcGIS.
4. Click Cancel on the Documentation Editor.
Selecting the best site
Youve discovered where the optimal sites are for building
the new school. All the locations in the opt_areasM layer
are suitable. The last step in this exercise is to locate the
best site out of the alternatives. The roads layer displays the
roads within the town of Stowe. By examining the
opt_areasM layer with the roads layer, youll see that there
are some suitable areas for the school site that are not close
to roads within the town. Youll first exclude these areas by
locating suitable sites that are intersected by roads. Then
youll locate the best site based on area. An optimal school
site is greater than 10 acres, or 40,469 square meters.
Youll first convert the opt_areasM raster to a feature class
inside a geodatabase so you can use the area field that is
generated. Youll then use the selection functionality within
ArcMap to select features that are intersected by roads.
Then youll identify the optimal site from the alternatives,
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based on area, and youll create a new feature class from
the selection that youll use in the next exercise.
1. In the Conversion Tools toolbox, expand the From Raster
toolset.
2. Right-click the Raster to Polygon tool and click Open.
3. Click the Input raster dropdown arrow and click the
opt_areasM raster layer.
4. Leave the default for the Field parameter as Value.
5. Click the Browse button, navigate to your
C:\Spatial\Results folder, and double-click site.mdb (the
personal geodatabase you created in the previous
exercise).
6. Type opt_areasM for the name of the feature class to
create inside the geodatabase, then click Save.
7. Leave the default checked to Simplify polygons. The
polygons will be simplified to reduce the stair-step
effect when a raster is converted to a polygon.
8. Click OK.
9. Leave the landuse, elevation, hillshade, destination,
rec_sites, schools, and opt_areasM (feature class)
layers in the table of contents. Click the rest of the
generated layers in the table of contents, right-click, and
click Remove. Press and hold the Shift key to select
multiple layers. Your ArcMap table of contents and
display should resemble the graphic below.
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10. Click Selection on the Main Menu and click Select By
Location.
11. Set up the dialog box as shown below. You want to
select features from opt_areasM that intersect roads.
12. ClickApply, then click Close.
All features that intersect roads are selected in the
display.
13. Click Selection on the Main Menu again and click Select
By Attributes.
14. Click the Layer dropdown arrow and click the layer
opt_areasM.
15. Click the Method dropdown arrow and click Select from
current selection.
16. Double-click [Shape_Area] from the Fields list to enter
the field in the expression text box.
17. Click the >= button.
18. Type a space, then type 40469.
19. Click Apply, then click Close.
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` There is one feature that fits the criteria of being equal
to or greater than 10 acres (40469 square meters).
20. Right-click opt_areasM, point to Selection, and click
Create Layer From Selected Features.
The added layer opt_areasM selection is an in-memory
layer that references the opt_areasM feature class.
Youll save it as a feature class on disk.
21. In the Data Management Tools toolbox, expand the
Features toolset.
22. Right-click the Copy Features tool and click Open.
A
23. Click the Input Features dropdown arrow and click the
opt_areasM selection layer.
24. Click the Browse button next to the Output Feature
Class parameter and navigate to
C:\Spatial\Results\Site.mdb.
25. Type final_site for the name of the output feature
class and click Save.
26. Click OK to run the tool.
A feature class is created and added to the table of con-
tents.
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27. Click opt_areasM in the table of contents, press the
Shift key and click opt_areasM selection.
28. Right-click and click Remove.
The final_site layer displays the location of the optimal site
for the new school.
29. Click File on the Main menu and click Save to save the
map document.
You have now completed Exercise 2. You can continue on
to Exercise 3, or you can stop and continue later.
Optimal site
for the new
school
QUICK-START TUTORIAL 47
Exercise 3: Finding an alternate access route to the new school site
In this exercise, you will find the best route for a new
access road. The steps you might follow to produce such a
path are outlined below.
Create the source dataset if necessary. The source is the
school site (the final_site feature class) you created in
Exercise 2.
Create the cost dataset by deciding which datasets are
required, reclassifying them to a common measurement
scale, weighting them, then combining them.
Perform cost distance analysis using the source and cost
datasets as inputs. The distance dataset created from this
tool is a raster in which the value of each cell is the accumulated
cost of traveling from each cell back to the source.
To find the least costly path, you need a direction dataset,
which can be created as an additional dataset from the Cost
Distance tool. This gives you a raster of the direction of the
least costly path from each cell back to the source (in this
exercise, the school site).
Create the destination dataset if necessary. In this exercise,
the destination dataset is a point at a road junction.
Perform cost path analysis using the distance and direction
datasets created from the Cost Distance tool.
This exercise will take approximately 15 minutes to com-
plete.
Setting up
If you are continuing on from the previous exercise and
have the Site Analysis map document open, skip the next
few steps and go to the next section, Creating a new
model.
1. Start ArcMap by either double-clicking a shortcut
installed on your desktop or using the Programs list in
the Start menu.
2. Click C:\Spatial\Site Analysis.mxd in the Browse for
maps list to open the map document created in the
previous exercise.
Creating a new model
Youll create a new model inside your Site Analysis Tools
toolbox called Find Best Route. This model will calculate
the best path through the landscape from the source (the
school site) to the destination point, taking into consideration
the slope of the land and the type of landuse the path will
cross.
1. Right-click the Site Analysis Tools toolbox, point to New,
and click Model.
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An empty ModelBuilder window will open.
2. Click the Model menu and click Model Properties.
3. Type find_route in the Name text box.
4. Type Find Best Route in the Label text box.
The name is used in scripting and at the command line.
The label is the display name for the model.
5. Check Store relative path names so that all paths for
sources of information referenced by the tool are saved
relative to the location of the toolbox. If the toolbox and
its data are moved, paths to data sources will be altered
accordingly.
6. Click the Environments tab and check the same environment
settings for this model as you did for the model
created in Exercise 2.
General Settings section: Check Current Workspace,
Scratch Workspace, and Output Extent.
Raster Analysis Settings section: Check Cell Size.
7. Click Values.
8. Expand General Settings and set:
Current Workspace = C:\Spatial
Scratch Workspace = C:\Spatial\Results
Output Extent = Same as Layer elevation
9. Expand Raster Analysis Settings and set Cell Size =
Same as Layer elevation.
10. Click OK on the Environment Settings dialog box.
11. Click OK on the Model Properties dialog box.
12. Click the Model menu and click Save.
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Creating the cost dataset
You created the source dataset in the previous exercise.
This is the location of the school site (your final_site layer).
Youll create the cost dataset that will identify the cost of
traveling over the landscape from any location back to the
school, based on the fact that it is more costly to traverse
steep slopes and construct a road on certain landuse types.
Deriving slope
It is difficult to build a road on steep slopes, so youll
calculate slope to take into consideration the slope of the
land.
1. In the Spatial Analyst Tools toolbox, expand the Surface
toolset.
2. Click and drag the Slope tool into the ModelBuilder
window.
An element that references the Slope tool is created in
the display window.
3. Right-click the Slope tool element and click Open.
4. Click the Input raster dropdown arrow and click the
elevation layer.
5. Accept the default path for the Output raster parameter
value and type slope_ex3 for the name. The default
path is set to the scratch workspace (for example,
C:\Spatial\Results) you set up earlier in the Environment
Settings dialog box.
6. As you did when calculating hillshade in Exercise 1, type
0.3048 for the value of the Z factor parameter to
convert the z values to the same unit of measure as the
x,y units (from feet to meters).
7. Click OK.
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8. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
The process is now colored in, meaning it is ready to
run.
9. Right-click the derived data element for the Slope tool
and click Rename.
10. Type Slope output and click OK.
11. Right-click the Slope output derived data element and
click Add To Display.
12. Right-click the Slope tool element and click Run to run
the process.
13. Examine the layer added to your ArcMap display. Steep
slopes are displayed in red, less steep slopes in green in
the output layer.
Reclassifying slope
It is preferable that the new road traverses less steep
slopes. You will reclassify the slope layer, slicing the values
into equal intervals. Youll give a value of 10 to the most
costly slopesthose with the steepest angle of slopeand
1 to the least costly slopesthose with the least angle of
slope, and rank the values in between linearly.
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1. In the Spatial Analyst Tools toolbox, expand the Reclass
toolset.
2. Click and drag the Reclassify tool into the ModelBuilder
window.
An element that references the Reclassify tool is
created in the display window.
3. Right-click the Reclassify tool element and click Open.
4. Click the Input raster dropdown arrow and click the
Slope output variable.
5. Accept the default for the Reclass field parameter so
the Value field will be used.
6. Click Classify.
7. Click the Method dropdown arrow and click Equal
Interval.
8. Click the Classes dropdown arrow and click 10.
Note: If you know specific break points between classes,
such as 5 percent, 10 percent, 15 percent, and so on, you
would enter them in the Break Values text box.
9. Click OK.
You want to avoid steep slopes when constructing the road,
so steep slopes should be given higher values in the cost
dataset. Because the default gives high values to steeper
slopes, you do not need to change the default New Values.
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10. Accept the default location for the value of the Output
raster parameter, but type Rslope_ex3 for the name.
11. Click OK.
12. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
13. Right-click the derived data element for the Reclassify
tool and click Rename.
14. Type Reclassed slope and click OK.
15. Right-click the Reclassed slope derived data element
and click Add To Display.
16. Right-click the Reclassify tool element and click Run to
run the process.
17. Examine the reclassed slope layer added to your
ArcMap display. It shows locations that are more costly
than others for constructing a roadhigher values
indicate the more costly areas that should be avoided.
Weighting and combining datasets
You will now combine the reclassed slope and landuse
datasets to produce a dataset of the cost of building a road
from each location in the landscape, in terms of steepness
of slope and landuse type. In this model, each dataset has
equal weight.
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1. In the Spatial Analyst Tools toolbox, expand the Overlay
toolset.
2. Click the Weighted Overlay tool and drag it into the
ModelBuilder window.
An element that references the Weighted Overlay tool is
created in the display window.
3. Right-click the Weighted Overlay tool element and click
Open.
The default evaluation scale is from 1 to 9 by 1. As in
Exercise 2, a scale of 110 was used when reclassifying
the slope dataset, so before adding input rasters to the
Weighted Overlay tool, youll set the evaluation scale from
1 to 10 by 1. This means you will avoid having to update the
scale values after adding your input slope dataset.
4. Type 1, 10, and 1 in the From, To, and By text
boxes.
5. Click the Add Raster Row button to add the input
rasters.
6. Click the Input raster dropdown arrow and click the
Reclassed slope variable.
7. Accept the default value for the Input field parameter
and click OK.
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The raster is added to the Weighted Overlay dialog box.
The Field column displays the values of the reclassified
slope output. The Scale Value column mimics the Field
column because the evaluation scale was set to encompass
the range of values in each input raster. Youll keep the
Scale Value values as they are, since they have already
been altered according to suitability.
8. Click the Add Raster Row button again to add the
landuse input raster.
9. Click the Input raster dropdown arrow and click the
landuse layer.
10. Click the Input field dropdown arrow and click Landuse.
11. Click OK.
Youll weight the scale values of the landuse layer so they
are comparable with your Reclassed slope derived dataset.
A higher value indicates that a particular landuse type is
more costly, and therefore, a less suitable location through
which to build a road.
12. Type the following scale values:
Brush/transitional5
Barren land2
Built up9
Agriculture4
Forest8
Water10
Wetlands10
Higher values indicate higher road construction costs.
Note: Take care using Restricted for the scale value when
creating a cost surface. Because using Restricted gives a
value to the cell that is the minimum value of the evaluation
scale minus 1, your restricted areas will appear to be given
the lowest cost when they are actually excluded from the
analysis. You should instead assign a high cost or set the
scale value to NoData for areas you want to exclude from
the analysis. If NoData is used, check first that there are no
areas of NoData in your input rasters. If there are, it will be
difficult to tell whether an area of NoData is there because
it was excluded or there was no original information at that
location for one of your inputs.
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Youll now assign an equal percentage of influence to each
raster, as they are all equally important.
13. Click Set Equal Influence to assign an equal percentage
of influence (50 percent each) for landuse and
Reclassed slope.
14. Accept the default path for the value of the Output
raster parameter, but type cost_surf for the name.
15. Click OK on the Weighted Overlay dialog box.
16. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
17. Right-click the derived data element for the Weighted
Overlay tool and click Rename.
18. Type Cost surface and click OK.
19. Right-click the Cost surface derived data element and
click Add To Display.
20. Right-click the Weighted Overlay tool element and click
Run to run the process.
21. Examine the layer added to your ArcMap display.
Locations with low values indicate areas that will be the
least costly to build a road through.
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Performing cost distance
You will now run the Cost Distance tool using the cost
dataset you just created (which identifies the cost of
traveling through each cell) and the final_site layer (the
source) you created in Exercise 2. The outputs from this
tool are a distance dataset in which each cell contains a
value representing the accumulated least cost of traveling
from that cell to the source and a backlink dataset that
gives the direction of the least costly path from each cell
back to the source. This conceptual process is explained in
more detail in Chapter 7 of Using ArcGIS Spatial Analyst.
1. In the Spatial Analyst Tools toolbox, expand the Distance
toolset.
2. Click and drag the Cost Distance tool into the
ModelBuilder window.
An element that references the Cost Distance tool is
created in the display window.
3. Right-click the Cost Distance tool element and click
Open.
4. Click the Input raster or feature source data dropdown
arrow and click the final_site layer.
5. Click the Input cost raster dropdown arrow and click the
Cost surface variable (the output from the Weighted
Overlay tool).
6. Accept the default path for the Output distance raster,
but change the name to cost_dist.
7. Type C:\Spatial\Results (or an alternative drive) for
the path of the Output backlink raster parameter, and
type cost_bklink for the name of the output.
8. Click OK.
9. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
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10. Right-click the cost_dist derived data element and click
Rename.
11. Type Output cost distance and click OK.
12. Right-click the Output cost distance derived data
element and click Add To Display.
13. Right-click the cost_bklink derived data element and
click Rename.
14. Type Output cost backlink and click OK.
15. Right-click the Output cost backlink derived data
element and click Add To Display.
With the Add To Display property checked, the derived
data referenced by these elements will be added to the
display each time the model is run.
16. Right-click the Cost Distance tool element and click Run
to run the process.
17. Examine the layers added to your ArcMap display. The
cost distance layer (cost_dist) displays the accumulated
cost of traveling from any location (or cell) to the
source (the school site), but it does not contain information
on which way to travel from a particular cell to the
source, just how much it will cost to get there, following
the least costly path. The cost backlink layer
(cost_bklink) shows which way to travel from any cell,
following the least costly path back to the source.
Finding the least costly path
The new road will redirect much of the traffic away from
the existing road to the school and provide a back route
for school buses and other vehicles.
1. Examine the destination point for the new road
(Destination.shp in the table of contents of your ArcMap
session). This is the starting point for the new road to
the school site.
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2. In the Spatial Analyst Tools toolbox, expand the Distance
toolset.
3. Click and drag the Cost Path tool into the ModelBuilder
window.
An element that references the Cost Path tool is created
in the display window.
4. Right-click the Cost Path tool element and click Open.
5. Click the Input raster or feature destination data
dropdown arrow and click the layer destination.
6. Click the Input cost distance raster dropdown arrow and
click the Output cost distance variable (one of the
outputs from the Cost Distance tool).
7. Click the Input cost backlink raster dropdown arrow and
click the Output cost backlink variable (one of the
outputs from the Cost Distance tool).
8. Accept the default path for the Output raster parameter,
but change the name to cost_path.
When the input feature destination data is processed, it
will be converted temporarily to a grid as part of the
processing. There will only be one cell in this grid,
because there is only one destination point. So the value
for the Path type parameter can be left as
EACH_CELL. Only one path will be created, since
there is only one cell.
9. Click OK.
10. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
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11. Right-click the cost_path derived data element and click
Rename.
12. Type Output cost path and click OK.
13. Right-click the Output cost path derived data element
and click Add To Display.
14. Right-click the Cost Path tool element and click Run to
run the process.
15. Remove the created layers slope_ex3, rslope_ex3,
cost_surf, cost_dist, and cost_bklink so you can see the
path displayed over the landuse and hillshade layers.
16. Examine the layer added to your ArcMap display. The
cost_path layer represents the least costly path from the
school site to the destination point. It avoids steep slopes
and certain landuse types considered to be more costly
for constructing the road.
As a last step in your model, youll convert the raster path
to a polyline for display purposes.
17. In the Conversion Tools toolbox, expand the From
Raster toolset.
18. Click and drag the Raster to Polyline tool into the
ModelBuilder window.
An element that references the Raster to Polyline tool is
created in the display window.
19. Right-click the Raster to Polyline tool element and click
Open.
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20. Click the Input raster dropdown arrow and click the
Output cost path variable.
21. Leave the default field as VALUE.
22. Click the Browse button next to the Output polyline
features parameter and navigate to your personal
geodatabase C:\Spatial\Results\Site.mdb.
23. Type new_route for the name of the feature class and
click Save.
24. Accept the defaults for all other parameters and click
OK.
25. Click the Auto Layout button, then click the Full Extent
button to apply the current diagram properties to the
elements and place them within the display window.
26. Right-click the new_route derived data element and
click Rename.
27. Type Output route and click OK.
28. Right-click the Output route derived data element and
click Add To Display.
29. Right-click the Raster to Polyline tool element and click
Run to run the process.
30. Examine the layer new_route that is added to your
ArcMap display. The raster path has been converted to
a polyline.
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Note: You can easily change parameter values to experiment
with different outcomes and rerun the model. Only the
processes in the model that are dependent on the output of
the process altered will need to be rerun. For example,
lowering the weight applied to cell values where the landuse
is built up from 9 to 1 will alter the potential path for the
new road considerablyit will tend to follow existing roads
where it can, which may be a cheaper option to consider.
Setting model parameters
As you did with the Find location for school model, youll
rename some of the variables and set them as model
parameters so they will display on the models dialog box.
1. Right-click the landuse project data element and click
Rename.
2. Type Input landuse raster and click OK.
3. Right-click the elevation project data element and click
Rename.
4. Type Input elevation raster and click OK.
5. Right-click the final_site project data element and click
Rename.
6. Type Input source and click OK.
7. Right-click the destination project data element and click
Rename.
8. Type Input destination and click OK.
9. Right-click Input landuse raster, Input elevation raster,
Input source, Input destination, and Output route and
click Model Parameter.
10. Click the Model menu and click Save.
11. Click the Model menu again, and click Close.
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Viewing the modeľs dialog box
1. Right-click the Find Best Route model in the ArcToolbox
window and click Open, or double-click the tool.
The variables you made into model parameters are
displayed as the parameters on the models dialog box.
Users of your model can simply enter their own parameter
values to find suitable routes from point A to point B
in their area without having to know much information
about the underlying workings of the model. As with the
Find location for school model, they would, of course,
have to have the same fields present in the landuse data,
understand the methodology of the model, and agree
with the assumptions applied.
2. Click Cancel on the models dialog box.
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Saving the map document
You have set relative paths for both models created in this
tutorial, so if the toolbox containing the models and the data
are moved (keeping the same structure between them) to a
new location on disk, the paths to the data sources will be
set relative to the position of the toolbox. You should also
set relative paths for your map document so layers in the
table of contents will find their data sources by traversing
the relative paths.
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1. Click File on the Main menu and click Map Properties.
2. Click Data Source Options.
3. Check Store relative path names and click OK.
4. Click OK on the Site_Analysis.mxd Properties dialog
box.
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5. Click File on the Main menu and click Save.
6. Click File on the Main menu and click Exit.
This brings you to the end of this tutorial. You have been
introduced to some of the tools available with Spatial
Analyst, both through the Spatial Analyst toolbar and the
SpatialAnalyst Tools toolbox. Youve learned how to build
models that are reusable and can be shared with others. In
particular, youve learned how to create a suitability map,
and youve learned how to calculate the least costly path
across a landscape. The sequences of steps involved can
be applied to many different applications.
There are many more tools that you can use to help you
perform your spatial analysis tasks. Using ArcGIS Spatial
Analyst will guide you as you learn how to solve your own
specific spatial problems. Explore the online Help system
for conceptual help for each toolset and help for each tool
in the SpatialAnalyst Tools toolbox, and consult
Geoprocessing in ArcGIS for more information on the
geoprocessing functionality withinArcGIS.
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