Crime beyond the edge: development of a tool to correct the edge effect on crime count

Abstract

The edge effect is a problem that can alter the results of some analyses, such as counting crime within a given geographic area. This article introduces a tool developed for ArcGIS toolbox, (ArcGIS Geographic Information System) to correct the border issues when using an aggregated crime data to artificially bounded space analytical units. It uses a method which considers those points located near the edge of the analysis unit, and avoids increasing the number of criminal points by assigning a value according to the distance of the edge. For this purpose, two functions based on decay with distance can be chosen: normal and linear. In order to show the performance of the tool, a sample of theft data occurred in 2016 in each census tract of Barcelona (Spain) district was used. These results show remarkable differences in the number of thefts in each census tract, before and after applying the edge correction. Some of the census tracts even went from experiencing no theft at all to having 5.5 or 4.5 incidents after correcting the edge effect. Finally, to demonstrate the benefits of the proposed tool, other strategies traditionally used as a solution for the edge effect were used. Then, the results are compared with those previously obtained.