Ron Wilson
University of Maryland, Baltimore County

ZIP Codes are commonly used for mapping, spatial analyses, creating tables, or other reporting products. Used for these tasks, the results from using these geographies often are distorted because of adverse statistical properties inherent with ZIP Codes. Summarizing ZIP Code data to other large geographies (for example, county, Core Based Statistical Area, state) associates them with these other geographies to create aggregate counts so that metropolitan or county rankings can be reported. This process requires ZIP Codes to be properly allocated to these other geographies to accurately associate a record with that area. Although some companies or government organizations already provide a crosswalk to these geographies, the allocation method used is unclear, leaving it indiscernible as to the accuracy of the assignment of ZIP Codes. In this article, we demonstrate how to use the U.S. Department of Housing and Urban Development (HUD) United States Postal Service ZIP Code Crosswalk Files to more directly control the ZIP Code allocation process of records to alternative geographies. In meeting this objective, we also provide results of an analysis using the HUD Crosswalk File in associating a ZIP Code with U.S. counties.