Exercise 10 Spatial Analyst The following steps describe the general process that you will follow to complete the exercise. Specific steps will be provided later in the step-by-step instructions component of the exercise. Review the exercise data. Use map algebra to identify areas of population change. Step-by-Step Instructions Task 1: Open ArcMap and activate the Spatial Analyst extension. Open ArcMap and indicate you want to work in A new empty map when prompted. From the Customize menu, choose Extensions to open the Extensions dialog box. Verify that the box to the left of Spatial Analyst extension is checked. ArcCatalog and create an address locator you will use to geocode the facility data.
The Spatial Analyst extension is one of many extensions available for use with the ArcGIS product. These extensions significantly expand the capabilities of ArcGIS. Many extensions are very specialized such as the Survey Analyst extension, which allows for the display and analysis of surveying data. Others, such as the Spatial Analyst extension, offer a suite of tools that can be used for a variety of purposes by many different types of users. To run the Spatial Analyst extension and most other extensions, you need to purchase a license from Esri. In the case of your student version of ArcGIS, you already have access to Spatial Analyst and many other extensions. Click Close to close the Extensions dialog box. From the Customize menu, choose Toolbars>Spatial Analyst to view the Spatial Analyst toolbar. Task 2: Open the map for this exercise. From the File menu, choose Open to open the browse window. Navigate to the EX10 folder and open the EX10 map document. This map pulls together the results of three tasks that have been completed in preparation for you to determine how the population distribution in Indianapolis, Indiana, has changed between 1990 and 2000.
Task 3: Explore the layers listed under the Data Collection section of the table of contents. If not already selected, check both the Tract1990 and Tract2000 layers under the Data Collection label. Uncheck and then recheck the visibility box next to the Tract2000 layer under the Data Collection label so you can see the way the census tract boundaries changed between 1990 and 2000. Remember that ArcGIS draws data from the bottom to the top of the table of contents. Thus, by turning on and off the census tract layers, you can see how they changed from one decade to the next. This project involved the collection of local census tract boundary data for 1990 and 2000. These two years of data represent the points in time for which you need to assess whether any population changes have occurred. The boundaries of these two years of data are not the same. This is especially true in the outer areas of the city an indication of where population has changed the most. Task 4: Explore the layers listed under the Data Manipulation section of the table of contents.
Check both of the visibility boxes next to the TractCentroid90 and TractCentroid00 Layers. Uncheck and then recheck the visibility box next to the TractCentroid90 layer under the Data collection group so you can see the distribution of census tract centroids for the 1990 and 2000 census tracts. To create a surface in Spatial Analyst, we need to create a series of points attributed with population counts by census tract. Creating the census tract centroids for each census tract was accomplished by calculating X and Y coordinates, and then exporting the event theme to a new geodatabase. The new geodatabases were joined (using the table join process you learned about earlier in the course) to information about population for each year. Feel free to open the attribute table for each layer if you want to see the population data. Uncheck both of the visibility boxes next to the TractCentroid90 and TractCentroid00 Layers. Task 5: Explore the layers listed under the Data Analysis labels in the table of contents. Click the visibility boxes next to the pop2000 and pop1990 layers under the Data Analysis label.
Observe that by checking and unchecking the pop2000 visibility box, you can see how population location changes between 1990 and 2000. Data analysis involved the creation of grids, using the Spatial Analyst Density tool. This tool uses points (in this case, the census tract centroids in Indianapolis, Indiana) to produce a grid that represents the distribution of sum phenomena (in this case population). The creation of these two grids was necessary because the process that you will complete in the remainder of the exercise requires data as the input. Task 6: Create a grid that illustrates the population change between 1990 and 2000. You will need to add a new folder to the existing folders in your EX10 file. Name the new folder Population. Do not put anything into the folder at this time. From the Search Window, type Raster Calculator as shown below.
Click Raster Calculator to open the tool. Enter the expression POPDIFF="Data Analysis\pop2000" - "Data Analysis\pop1990" in the Raster Calculator. Change the Output raster to EX10\Population\POPDIFF. The Raster Calculator should appear as follows. This expression creates a grid named POPDIFF that is the result of taking the difference between the values in the POP200 grid and the values in the POP1990 grid.
Click the OK button to execute the calculation and create a new grid named POPDIFF.
Right-click the POPDIFF layer and choose Properties to open the Properties dialog box. Click the Symbology tab to view the symbology options. Click the Classified Option. You may be asked in you want to create a histogram. Click Yes to create the histogram.
Change the number of classes to 9. Left-click the Label Title and choose Format Labels to open the Number format window. Change the number of decimal places to 1. Click OK to close the Number Format window. Click the Classify button to open the Classification window. Change the Method to Manual.
Starting with the highest value, modify the Break Values on the right side of the Classification window symbols to those shown below. Click OK to close the classification dialog box. Change the colors assigned to the negative (-) values to shades of red, with the darkest shade being assigned to the lowest number. Change the colors assigned to the positive numbers to shades of blue, with the darkest shade being assigned to the highest number.
This color scheme should clearly show areas of growth and decline in population. Click OK on the Layer Properties dialog box to save your changes and update the map as shown below. You may want to turn off all of the layers but the POPDIFF layer so that you can clearly see how the population has changed between 1990 and 2000. The map clearly delineates areas of growth and areas of decline in population across the City of Indianapolis.
Save your changes to the EX10 map document. Create a Thematic Map using this document. Apply an appropriate title, legend, cartographic North, and your name. Export your new map as a PDF and attach it to this week s discussion thread. Summary This exercise was designed to help you explore how the Spatial Analyst extension can be used to answer questions that are important to emergency managers. If you would like to learn more about this powerful technology, you can either participate in additional classroom courses or you can explore the detailed documentation that is provided with ArcGIS Spatial Analyst.