IV. a. Spatial Analyst-Density
Estimated time:
2 minutes
As a traffic engineer, safety is one of the main concerns. The identification of high crash density locations is therefore necessary
This exercise will help you:
- a1. Add spatial analyst tool
- a2. Add Density function
- a3. Determine the high crash density locations
Text Version:
- Go to “View” in the application tool bar and select “Data view”
- On the standard tool bar select the “Zoom to full extent”
- [Left] Click on “Tools” on standard tool bar and click on “Extensions”
- a1: Check “Spatial Analyst” and Close
- a1: [Left] Click on “Tools” on standard tool bar and click on “Customize”
- a1: [Left] Click on “Commands” and scroll down in “Categories” and click on “Spatial Analyst”
- a2: On the right side of “Categories” on “Commands” list click “Density” and drag it to the “Tools”
- a2: On the right side of “Categories” on “Commands” list click “Zonal Statistics” and drag it to the “Tools” and click “Close”
- a3: Uncheck all layers except “All_Crashes_04-06” layers and “ADMIN_COUNTIES_AHTD_2005_poly” layer
- a3: Drag and drop the “All_Crashes_04-06” layer to the top
- a3: Right Click on the “All_Crashes_04-06” click on “Joins and Relates”, click on “Remove Join(s)” and select “Remove all Joins”
- a3: [Left] Click on “Density” and in the “Input Data” select “All_Crashes_04-06”
- a3: In the “Population Field” select the “CRASHSEVER”
- a3: Check “Kernel” in “Density Type”
- a3: In the “Search radius” enter “15000”
- a3: In the “Output cell size” enter “1000”
- a3: In the “Output Raster” browse a folder and save by giving an appropriate character name
- a3: Drag and drop the new layer to the second top of the list
- a3: Right click on the “All_Crashes_04-06” layer and click on “Display” and in the “Transparency” enter “80” click “Apply”, the “All_Crashes_04-06” layer should be on the top of all layers list
- a3: Right click on the“ADMIN_COUNTIES_AHTD_2005_poly” layer and click on “Display” and in the “Transparency” enter “80” click “Apply”
- a3: Right click on the new layer and click on “Display” and in the “Transparency” enter “40” click “Apply”
- a3: Right click the new layer and select “Save as Layer File..” and save the layer in an appropriate location and give the layer a name of your choice
- a3: Right click on the new layer and then click on “Properties”, select “Symbology” in the “Show” region select “Classified”, on the right side of the “Classified” in the “Color Ramp” drag down and select an appropriate color scheme
- a3: [Left] Click “Apply”
- a3: Select the “Label” field and by click on each value in the “Label” delete the decimal places
- a3: [Left] Click “Apply”
- a3: [Left] Click “Ok”
(Note: Density type is Simple, and if the input is points, density calculates the density of point features around each output raster cell. Conceptually, a neighborhood is defined around each raster cell center, and the number of points that fall within the neighborhood is totaled and divided by the area of the neighborhood. If a population field setting other than none is used, the population field value determines the number of times to count the point.
Density type is Kernel; conceptually a smooth curved surface is fitted over each point feature. The surface value is highest at the location of the point, and diminishes with increasing distance from the point, reaching zero at the search radius distance from the point. The volume under the surface equals the population field value for the point, or one if none is specified. The density at each output raster cell is calculated by adding the values of all Kernel surfaces when they overlay the raster cell center)