Exercise 2: Finding a site for a new school in Stowe, Vermont, USA

In this exercise you will find suitable locations for a new Step 1
school. The four steps to produce such a suitability map are Landuse Elevation Recreation Schools
outlined below.

Decide which datasets you need as

Step 1: inputs. The datasets you will use in
Input Datasets this exercise are displayed to the
right.
Step 2
Calculate Slope Find Distance Find Distance
Step 2: Derive datasets. Create data from
existing data to gain new informa-
Derive Datasets
tion.

Step 3: Reclassify each dataset to a com-

Reclassify mon scale—for example, 1–10— Step 3
Datasets giving higher values to more suitable
Reclassify Reclassify Reclassify Reclassify
attributes.

Step 4: Weight datasets that should have

Weight and more influence in the suitability
Combine model if necessary, then combine
Datasets them to find the suitable locations.
Step 4

Your input datasets in this exercise are Landuse, Elevation,

Recreation Sites, and Existing Schools. You will derive Weight and Combine Datasets
slope, distance to recreation sites, and distance to existing
schools, then reclassify these derived datasets to a common
scale from 1–10. You will then weight them according to a
percentage influence and combine them to produce a map
displaying suitable locations for the new school. The
diagram to the right shows the process you will take.

QUICK-START TUTORIAL 23
Step 1: Inputting datasets

1. Click the Add Data button on the Standard toolbar. Setting the analysis properties
Set up the analysis options like you did in Exercise 1.
1. Click the Spatial Analyst dropdown arrow and click
Options.
1 2. Specify a working directory on your local drive in
which to place your analysis results. Type c:\spatial to
2. Navigate to the folder on your local drive where you create a folder called spatial on your C:\ drive.
installed the tutorial data (the default installation path is 3. Click the Extent tab.
ArcGIS\ArcTutor\Spatial, on the drive where the tutorial
4. Click the Analysis Extent dropdown arrow and click
data is installed).
Same as Layer “landuse”.
3. Click elevation, then click and hold down the Ctrl key
5. Click the Cell Size tab.
and click landuse, rec_sites, and schools.
6. Click the Analysis Cell Size dropdown arrow and click
4. Click Add.
Same as Layer “elevation”.
7. Click OK on the Options dialog box.
3 2

Each dataset is added to the ArcMap table of contents

as a layer.

24 USING ARCGIS SPATIAL ANALYST

Step 2: Deriving datasets

Deriving data from your input datasets is the next step in 3. Type slope in the Output raster text box to permanently
the suitability model. You will derive the following: save your output slope dataset to the location of your
• Slope from elevation working directory (c:\spatial).

• Distance from recreation sites You will use this dataset again in Exercise 3.

• Distance from existing schools Note: A copy of this slope dataset can be found in the
location ArcGIS\ArcTutor\Spatial\Results\Ex2\Slope.
Deriving slope 4. Click OK.
Since the area is mountainous, you need to find areas of
relatively flat land to build on, so you will take into consid- 2
eration the slope of the land.
1. Click the Spatial Analyst dropdown arrow, point to
Surface Analysis, and click Slope.

1
3 4
The output slope dataset will be added to your ArcMap
session as a new layer. High values—red areas—
indicate steeper slopes.

2. Click the Input surface dropdown arrow and click

elevation.

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 3. Click OK.

Deriving distance from recreation sites

In this model, it is preferable that the school be built near 3
recreational facilities, so you will now calculate the
straight-line distance from Recreation Sites.
The output distance to the rec_sites dataset will be
1. Click the Spatial Analyst dropdown arrow, point to added to your ArcMap session as a new layer. Values of
Distance, and click Straight Line. zero indicate the location of a recreation site, with
values—distances—increasing as you move away from
each of these sites.

2. Click the Distance to dropdown arrow and click

rec_sites.
Leave the defaults for all other options.

26 USING ARCGIS SPATIAL ANALYST

Note: A copy of this distance to rec_sites dataset can be The output distance to schools dataset will be added to
found in the location your ArcMap session as a new layer.
ArcGIS\ArcTutor\Spatial\Results\Ex2\recD.
4. Uncheck the box next to Schools to turn off this layer so
you only see the locations of the recreation sites and the
distance to them.

Deriving distance from schools

You will now derive a dataset of distance from existing
schools. It is preferable to locate the new school away from
existing schools to spread out their locations through the
town.
1. Click the Spatial Analyst dropdown arrow, point to
Distance, and click Straight Line.
2. Click the Distance to dropdown arrow and click schools. 4. Check the box next to the schools layer to turn it back
Leave the defaults for all other options. on and uncheck the box next to rec_sites to turn this
layer off so you only see the locations of the schools and
3. Click OK. the distance to them.
Note: A copy of this distance to schools dataset can be
2 found in the location
ArcGIS\ArcTutor\Spatial\Results\Ex2\schD.

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Step 3: Reclassifying datasets

You now have the required datasets to find the best location
for the new school. The next step is to combine them to
find out where the potential locations can be found.
In order to combine the datasets, they must first be set to a
common scale. That common scale is how suitable a
particular location—each cell—is for building a new school.
You will reclassify each dataset to a common scale, within
the range 1–10, giving higher values to attributes within 1
each dataset that are more suitable for locating the school:
• Reclassify slope
• Reclassify Distance to recreation sites
• Reclassify Distance to schools 2
• Reclassify landuse

Reclassifying slope
It is preferable that the new school site be located on
relatively flat ground. You will reclassify the Slope layer, 3
giving a value of 10 to the most suitable slopes—those with
the lowest angle of slope—and 1 to the least suitable
slopes—those with the steepest angle of slope.
1. Click the Spatial Analyst dropdown arrow and click
Reclassify.
2. Click the Input raster dropdown arrow and click Slope.
3. Click Classify.

28 USING ARCGIS SPATIAL ANALYST

4. Click the Method dropdown arrow and click Equal 7
Interval.
5. Click the Classes dropdown arrow and click 10.
6. Click OK.

5 4

The output reclassified slope dataset will be added to your

6 ArcMap session as a new layer. Locations with higher
values—less-steep slopes—are more suitable than locations
You want to reclassify the Slope layer so steep slopes with lower values—steeper slopes.
are given low values, as these are least suitable for
building on.
7. Click the first New value record in the Reclassify dialog
box and change it to a value of 10. Give a value of 9 to
the next New value, 8 to the next, and so on. Leave
NoData as NoData.
8. Click OK.

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Note: A copy of this reclassified slope dataset can be found 2
in the location
ArcGIS\ArcTutor\Spatial\Results\Ex2\slopeR.

Reclassifying distance to recreation sites

The school should be located near recreational facilities. 3
You will reclassify this dataset, giving a value of 10 to
areas closest to recreation sites—the most suitable loca-
tions—giving a value of 1 to areas far from recreation
sites—the least suitable locations—and ranking the values
in between. By doing this you will find out which areas are
near and which areas are far from recreation sites.
1. Click the Spatial Analyst dropdown arrow and click
Reclassify. 4. Click the Method dropdown arrow and click Equal
Interval.
5. Click the Classes dropdown arrow and click 10.
6. Click OK.

5 4

2. Click the Input raster dropdown arrow and click

Distance to rec_sites.
3. Click Classify.

30 USING ARCGIS SPATIAL ANALYST

 You want to locate the school near recreational facilities, The output reclassified distance to recreation sites
so you will give higher values to locations close to dataset will be added to your ArcMap session as a new
recreational facilities, as these are the most desirable. layer. It shows locations that are more suitable for
7. As you did when reclassifying the Slope layer, click the locating another school. High values indicate more
first New value record in the dialog box and change it to suitable locations.
a value of 10. Give a value of 9 to the next New value, 8
to the next, and so on. Leave NoData as NoData.
8. Click OK.

Note: A copy of this reclassified distance from recreation

sites dataset can be found in the location
ArcGIS\ArcTutor\Spatial\Results\Ex2\recR.
8

QUICK-START TUTORIAL 31
Reclassifying distance to schools 2
It is necessary to locate the new school away from existing
schools in order to avoid encroaching on their catchment
areas. You will reclassify the Distance to schools layer,
giving a value of 10 to areas away from existing schools—
the most suitable locations—giving a value of 1 to areas 3
near existing schools—east suitable locations—and ranking
the values in between. By doing this you will find out
which areas are near and which areas are far from existing
schools.
1. Click the Spatial Analyst dropdown arrow and click
Reclassify.
4. Click the Method dropdown arrow and click Equal
Interval.
5. Click the Classes dropdown arrow and click 10.
6. Click OK.

5 4
1

2. Click the Input raster dropdown arrow and click

Distance to schools.
3. Click Classify.

32 USING ARCGIS SPATIAL ANALYST

 You want to locate the school away from existing
schools, so you will give higher values to locations
farther away, as these locations are most desirable.
As the default gives high New values—more suitable—
to high Old values—locations farther away from existing
schools—you do not need to change any values this
time.
7. Click OK.

Note: A copy of this reclassified distance from schools

dataset can be found in the location
ArcGIS\ArcTutor\Spatial\Results\Ex2\schR.

The output reclassified distance to schools dataset will

be added to your ArcMap session as a new layer. It
shows locations that are more suitable for locating
another school. Higher values indicate more suitable
locations.

QUICK-START TUTORIAL 33
Reclassifying landuse You will now remove the Water and Wetland attributes
and change their values to NoData.
At a town planners meeting it was decided that certain
landuse types were better for building on than others, 5. Click the row for Water, press the Shift key, click
taking into consideration the costs involved in building on Wetlands, then click Delete Entries.
different landuse types. 6. Check Change missing values to NoData.
You will now reclassify landuse. A lower value indicates All values for Water and Wetlands will be changed to
that a particular landuse type is less suitable for building NoData.
on. Water and Wetlands will be given NoData as they
7. Click OK.
cannot be built on and should be excluded.
1. Click the Spatial Analyst dropdown arrow and click
Reclassify. 4 2

1 5

2. Click the Input raster dropdown arrow and click landuse.

3. Click the Reclass field dropdown arrow and click
Landuse. 6 7
4. Type the following values in the New values column:
Agriculture—10 Built up—3
Barren land—6 Forest—4
Brush/Transitional—5

34 USING ARCGIS SPATIAL ANALYST

 The output reclassified landuse dataset will be added to 9
your ArcMap session as a new layer. It shows locations
that have landuse types that are considered to be better
than others for locating the school—higher values
indicate more suitable locations.

W Q
Note: A copy of this reclassified landuse dataset can be
found in the location
ArcGIS\ArcTutor\Spatial\Results\Ex2\landuseR.
8. Right-click Reclass of landuse in the table of contents
and click Properties.
9. Click the Symbology tab.
10. Click the Display NoData as dropdown arrow and click
Arctic White to show NoData values—Water and
Wetlands—in this color.
11. Click OK.

QUICK-START TUTORIAL 35
Step 4: Weighting and combining datasets

After applying a common scale to your datasets, where

higher values are given to those attributes that are consid-
ered more suitable within each dataset, you are ready to
combine them to find the most suitable locations.
If all datasets were equally important, you could simply
combine them at this point; however, you have been
informed that it is preferable to locate the new school close
to recreational facilities and away from other schools. You
will weight all the datasets, giving each a percentage 1
influence. The higher the percentage, the more influence a
particular dataset will have in the suitability model.
You will give the layers the following percent influence: 2. Double-click Reclass of Distance to rec_sites from the
(Each percentage is divided by 100 to normalize the Layers list to add it to the expression box.
values.) 3. Click Multiply.
Reclass of Distance to rec_sites: 0.5 (50%) 4. Click 0.5.
Reclass of Distance to schools: 0.25 (25%) 5. Click Add.
Reclass of landuse: 0.125 (12.5%) 6. Double-click Reclass of Distance to schools.
Reclass of slope: 0.125 (12.5%) 7. Click Multiply.
1. Click the Spatial Analyst dropdown arrow and click 8. Click 0.25.
Raster Calculator.
9. Click Add.
10. Double-click Reclass of landuse.
11. Click Multiply.
12. Click 0.125.
13. Click Add.
14. Double-click Reclass of slope.
15. Click Multiply.

36 USING ARCGIS SPATIAL ANALYST

16. Click 0.125. 18. Right-click the newly created raster layer in the table of
17. Click Evaluate to perform the weighting and combining contents and click Properties.
of the datasets. 19. Click the Symbology tab.
20. Click Classified from the Show list.
21. Click the Classes dropdown arrow and click 10.
22. Scroll to the last three classes, click one, then press and
hold the Shift key and click the other two.
23. Right-click the highlighted classes, click Properties for
selected Colors, and click a bright color.
24. Click the Display NoData as dropdown arrow and click
the color black. This displays values of NoData—Water
and Wetlands—in this color.
25. Click OK.

A P S

The output raster dataset shows you how suitable each

location is for locating the new school, according to the
criteria you set in the suitability model. Higher values
indicate locations that are more suitable.
The suitable locations are those areas that are close to
recreation sites, away from existing schools, on rela- D
tively flat land, and on certain types of landuse. The
higher weightings set for Distance to schools and
G
Distance to rec_sites have a powerful influence on
deciding which areas are more suitable than others.
F H

QUICK-START TUTORIAL 37
 You decide that there are three main potential areas for Note: A copy of this Suitability dataset can be found in
locating the school. They are labeled in the diagram the location
below. ArcGIS\ArcTutor\Spatial\Results\Ex2\Suitability.
29. Click the output raster twice slowly. Rename the layer
Area 1 Area 2 Area 3 Suitability.

You decide that the best location is somewhere within Area

1, as there are three recreation sites in the neighboring area,
the ski resort being one of them. Also, although you know
that a considerable volume of traffic already uses the
current access road to this potential site, you are involved
in plans for constructing an alternative road to this area,
which will help alleviate the volume of traffic on the
current access road.
30. Click the Schools layer in the table of contents, press
the Ctrl key, and click all other layers except Suitability
You should now assess these locations to see which (use the scroll bar to move down the table of contents).
might be the best location. This should be done in the 31. Right-click one of the highlighted layers and click
field, as well as by examining the data you have on each Remove.
potential area. You have now completed Exercise 2. You can continue on
26. Right-click the output layer in the table of contents and to Exercise 3, or you can stop and continue later. Which-
click Make Permanent. ever option you choose, save the map document at this
27. Navigate to the folder on your local drive where you set point. Click the File menu and click Save As. Navigate to
up your working directory (c:\spatial). the location where you set up your local working directory
28. Type Suitability and click Save. (c:\spatial), specify a filename for the map document—
The temporarily created dataset will now be perma- Spatial_Tutorial—and click Save.
nently stored on disk.

38 USING ARCGIS SPATIAL ANALYST