* indicates required field
NAACCR uses the ANSI/FIPS code in the geocoded fields as geographical identifiers for state, county, census tract and block groups (NAACCR data item numbers: 81-84, 94-97, 110, 125, 130, 135, 361, 362, 363, 368). These codes are used to link to area-based attribute information, such as census tract poverty or rural-urban commuting area (RUCA).
Proper identification of these fields is critical to support small area analysis as well as health equity research. ANSI/FIPS codes are only unique to the location if all boundaries are only unique when nested within larger geographies. For instance, a 6-digit census tract is not unique. But the 6 digits associated with a 3-digit county is unique within the state.
Because these codes, particularly the census tracts, often have leading and trailing zeros which can be inadvertently dropped, it is recommended to transfer within the NAACCR layout, with the ANSI/FIPS codes as characters, or as a merged field that includes all geographies in one geolocation ID (i.e., a 12-digit field with state, county, tract, and block group concatonated).
While the ANSI/FIPS codes are continuously updated, the most significant updates occur in preparation for the decennial census. The NAACCR geocoder uses the ANSI/FIPS lists associated with the decennial census and does not update the list of ANSI/FIPS codes in between censuses in order to maintain continuity over time. Occasionally, county boundaries will change in between censuses, but NAACCR will continue to use the old county codes and boundaries to calculate rates until the next decennial census provides the associated denominator data for the new county codes and boundaries.
For more information, refer to the links below:
- Overview of the codes: https://www.census.gov/library/reference/code-lists/ansi.html
- List of codes down to block group, by state to 2010: https://www.fcc.gov/general/2010-census-blocks-state