Merging Zip Codes with Census Data
One of the most common and useful units of geographic analysis for our business clients and other types of organizations is zip code. That’s because we typically have residential or business addresses for their customers and prospects, and also because zip codes demarcate relatively small areas, are easy to map, and are familiar to most people.
But what happens when we want to analyze market segments and zip code areas by referencing some of the amazing, public data that is available from the Census Bureau? Ugh, they don’t use zip codes. The census aggregates data at “block group” levels and “census tract” levels, and then at other larger units including counties and states.
For many years we cobbled together our own mapping of zip codes to census tracts for local geographic analyses. Then we discovered this: the HUD USPS ZIP Code Crosswalk Files. The what? They are an incredibly handy (small and manageable) set of excel files that map every U.S. zip code to corresponding census tract(s) and vice versa. There are also files that map zip codes to county codes, and to other census aggregating units.
Wait, it gets even fancier. Because many zip codes overlap multiple census tracts, the files also indicate the proportion of residential and business addresses within each of those overlaps. As the HUD website notes, this may be useful if your unit of analysis is a housing unit or address: “By using an allocation method based on residential addresses rather than by area or by population, analysts can take into account not only the spatial distribution of population, but also the spatial distribution of residences.”
The file is updated four times a year with the latest zip code data from the U.S. Postal Service. Best of all, the data are free, and publicly accessible. Here’s to never cobbling together zip code mapping files, or paying some cheap data service for their outdated files, ever again!