How to Read the HUD-USPS ZIP Crosswalk Files:
There are twelve types of crosswalk files available for download. The first six crosswalk files are used to allocate ZIP codes to Census Bureau geographies such as census tracts, counties, county subdivisions, Core Based Statistical Areas (CBSAs), CBSA Divisions, and Congressional Districts. The last six are used to allocate from those same Census Bureau geographies to ZIP Codes. It is important to note that the relationship between the two types of crosswalk files is not perfectly inverse. That is to say, the ZIP to Tract crosswalk file cannot be used to allocate data from census tract geographies to ZIP codes. Instead, the Tract to ZIP crosswalk file must be used in that specific scenario.
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