Spatial Diffusion Processes

Abstract

This article proposes a new method for examining dynamic changes in the spatial distribution of a phenomenon. Recently introduced exploratory spatial data analysis (ESDA) techniques provide social scientists with anew set of tools for distinguishing between random and nonrandom spatial patterns of events (Anselin, 1998). Existing ESDA measures, however, are static and do not permit comparisons of distributions of events in the same space but across different time periods. One ESDA method—the Moran scatter plot—has special heuristic value because it visually displays local spatial relationships between each spatial unit and its neighbors. Weextend this static cross-sectional view of the spatial distribution of events to consider dynamic features of changes over time in spatial dependencies. The method distinguishes between contagious diffusion between adjoining units and hierarchical diffusion that spreads broadly through commonly shared influences. We apply the method to homicide data, looking for evidence of spatial diffusion of youth-gang homicides...