Zip codes and spatial analysis: Problems and prospects

The use of zip codes for spatial, demographic, and socio-economic analysis is growing. As of August 2005, 193 articles were indexed by “zip code” in the Social Sciences Citation Index, while 386 were indexed in PubMed. All of these articles were published since 1989. While the treatment of zip codes as units of analysis varies widely in epidemiology, marketing, geography, and the socio-economic planning sciences, there are a number of common “errors” that could be avoided if analysts retained a better understanding of zip code characteristics. The purpose of this paper is to outline the problems and prospects of utilizing zip codes for spatial analysis. Issues associated with spatial contiguity, data aggregation, and boundary definitions are addressed. Results suggest that, although zip codes are not the most robust spatial units of analysis available, they retain a modest degree of utility for specialized applications. Recommendations for future research regarding zip codes and their use in socio-economic applications are offered.