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COUNTYNHG
County (NHGIS code, identifiable counties only)
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Description

COUNTYNHG identifies the county where the household was enumerated, using the IPUMS National Historical Geographic Information System (NHGIS) coding scheme.

Researchers can use this variable to match IPUMS USA data with county-level GIS boundary files or aggregate data tables from the NHGIS website.

Codes

COUNTYNHG codes are 7-character county identifiers. The first 3 characters give the NHGIS state code and the last 4 characters give the NHGIS county code.

Because COUNTYNHG codes include both state and county codes, they distinguish each county uniquely for the entire country, not just within each state. This differs from the county codes given by COUNTYICP and COUNTYFIP, which are state-dependent.

NHGIS county-level boundary files and data tables include a code that matches COUNTYNHG in a field named "GISJOIN". Specifically, the GISJOIN codes in NHGIS files consist of a "G" character followed by the COUNTYNHG codes. The "G" prefix helps ensure that the codes are properly interpreted as text values (and not as numbers) in GIS and spreadsheet software. If the codes are converted to numbers, they lose leading zeros (e.g., "0600030" becomes 600030) and no longer match properly with the correct text versions of the codes.

User Note: A small number of cases in IPUMS USA microdata cannot be matched to counties or states in NHGIS. These cases have COUNTYNHG codes of 9999999. In the cases where the state can be identified, IPUMS provides the two-digit state FIPS code with trailing 9's. These cases are typically non-county areas such as Indian reservations and military installations.

A small number of NHGIS counties also cannot be matched to IPUMS USA microdata. These were counties with very small populations that were not captured by the microdata sampling procedures.

Comparability

COUNTYNHG is year-specific. Codes can have different meanings depending on the census year. Researchers should be careful to match IPUMS USA and NHGIS data only from the same year.

Universe

  • All households and group quarters.

Availability

United States
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  • 1930: All samples
  • 1920: All samples
  • 1910: All samples
  • 1900: 5%; 1%; 1.2% ovrsmp
  • 1880: All samples
  • 1870: All samples
  • 1860: All samples
  • 1850: All samples
Puerto Rico
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  • 1990: --
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  • 1930: --
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Flags

This variable has no flags.

Editing Procedure

There is no editing procedure available for this variable.