Economics
FIPS Codes, ZCTAs and the Plumbing of U.S. Geographic Data
If you've ever tried to join Census data to a map and gotten lost, the problem is almost always a FIPS or ZCTA mismatch. Here's the plain-English guide.
By City Zip Compare Editorial · December 14, 2025 · 5 min read
Federal Information Processing Standards (FIPS) codes are the IDs the U.S. government assigns to geographic units. States get two-digit codes (Florida is 12, California is 06). Counties get three-digit codes within their state. ZIP Code Tabulation Areas use the five-digit ZIP.
The most common joining mistake
FIPS codes contain leading zeros. If you load them into Excel or a CSV without forcing string type, those zeros disappear and your joins silently break. Alabama becomes 1 instead of 01; Alaska becomes 2 instead of 02. Always treat FIPS as text.
ZIPs have the same problem in the Northeast — 02101 (Boston) becomes 2101.
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Source: U.S. Census Bureau, American Community Survey 5-year estimates. Data: census.gov/programs-surveys/acs.