Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Points and Density

While we are on the subject of making surfaces and areas out of points, let’s consider the Density tool. This tool’s procedure takes the values that are associated with points and, with a raster, spreads them out over the landscape around the points. For example, suppose that you have data that places all the population of some lightly populated counties in a state at the points designated as courthouses. Obviously, everyone in a county doesn’t live at the courthouse. We will spread them out over a rectangular area (to make checking the results easier).

____ 17. Start a new map. Add as data Known_Populations.shp.7 Look at its attribute table, then close it. Label each point with the Population value, in green, size 12. Make the map units and the display units Kilometers. Approximately how far apart are the courthouses (population centers)? ________ kilometers. What we will do is spread the population at each courthouse over an area of several hundred square kilometers, just to illustrate how the Density tool works.

____ 18. Find the Point Density tool (Spatial Analyst > Density) in ArcToolbox. Start the tool. The Input Point Features would be Known_Populations. The Population field is just called Population. Make the Output raster Density_test, in

___IGIS-Arc_YourInitials\Experiment_with_Interpolation\Surfaces.gdb

using an output cell size of 1.0 kilometer on a side. For the neighborhood (populated area of the county), pick Rectangle. For the Neighborhood ...