This article explains how the Environmental Systems Research Institute’s (ESRI's) districting tool can be used as a free extension for ESRI’s ArcGIS Desktop to enable analysts to create new police districts in a city or region.
The ESRI districting tool requires an agency to have GIS (geographic information systems) data entered as a polygon feature class with attribute data. These polygons must be smaller than the intended districts. Analysts should use polygons that coincide with naturally occurring boundaries and main thoroughfares. The process of joining incident data to polygons in ArcGIS to achieve a count of incidents in each region is the same process that an analyst would use to create a choropleth map that depicts different incident counts. This article describes the five steps an analyst uses to join incident data to a polygon feature class. Instructions are also provided for downloading and installing the districting extension to ArcGIS Desktop. A “help” file and tutorial data are included with the installation. Fourteen steps are listed for analysts in creating a new districting plan. Once a districting plan has been created and the editing process begins, the districting toolbar becomes active, and smaller polygons can be grouped into districts. Redistricting should be an iterative process by which decisionmakers can gather input and create temporary selections, examining statistical output for each scenario. Districting can be accomplished by selecting a district from the dropdown list. Simple selection tools can be used to allot smaller polygon groups to a district. In describing advanced use of the districting tool, the author advises that analysts should examine which other data fields can be joined to the polygon and consider what statistical breakdowns are required for the command staff to make decisions. 3 figures and 4 notes