Crosswalking ZIP Codes to Census Geographies: Geoprocessing the U.S. Department of Housing & Urban Development's ZIP Code Crosswalk Files

[...]we compare the estimates from the crosswalk process with the actual data to gauge the level of accuracy as an indicator of reliability. General Approach to Crosswalking the ZIP Code Files Linking ZIP Code data to any of the ZIP Code crosswalk data sets is not a one-to-one assignment with any of the available geographies HUD offers.5 Rather, a many-to-many approach must be used to ensure each record's proportion in a crosswalk file is associated with the corresponding geography each ZIP Code is contained within or with which it overlaps. [...]when a ZIP Code is assigned to one tract, all the adjacent tracts associated with that same ZIP Code are not assigned any of the address ratios used for analysis. Once joined, a new field is calculated that is the product of the ZIP Code frequency and the tot_ratio field to produce an estimate for 311 rat calls for service. Because ZIP Codes cross-cut multiple counties, duplicate ZIP Code records appear in the crosswalk file, indicating multiple overlaps.