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NHGISJOIN
United States, County GIS identifier

Codes

NHGISJOIN is a 7-digit numeric variable.

A small number of cases in NAPP cannot be matched to the NHGIS. These are coded as 9999999 in NHGISJOIN. These were non-county areas such as Indian reservations and military installations. There were 6 such counties in 1900 and 1 in 1910.

A small number of counties in NHGIS cannot be matched to NAPP data for the United States. In all cases, these were very small counties that were not captured by the IPUMS sampling procedures. All of these counties contained fewer than 1,000 people; many were administrative areas with no population at all. There were 9 such counties in 1850, 56 in 1860, 32 in 1870, 33 in 1880, 2 in 1900 and 1910, and none in 1920 and 1930.

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