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TL,DR: Census Geographic Identifiers (GEOIDs)

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mattbarger edited this page Feb 19, 2019 · 5 revisions

Census Tracts

Census tract GEOID codes add specificity as the GEOID gets longer. More information here, but just to quickly explain, the GEOID of 11001005800 should be read as: 11-001-005800, or:

  • 11 - State FIPS code for District of Columbia
  • 001 - County FIPS code for District of Columbia (001 == DC has no counties)
  • 005800 - Tract code for tract 580.0 (one of four tracts that intersect the ZIP Code 20005 [where you are right now!])

To extend the example for a state-specific entity: A fire occurred recently at the 2900 block of Brierdale Lane in Bowie, Maryland. From the handy-dandy Census GeoCoder application we have the GEOID of the area as: 24033800504, which translates as:

  • 24 - State FIPS code for Maryland
  • 033 - County FIPS code for Prince George’s County
  • 800504 - Census Tract number.

As a general rule, however, CENSUS TRACTS ARE MUCH SMALLER THAN ZIP CODES. Take, for instance, the tracts contained within ZIP code 20715 in Bowie, Maryland:

> zcta_tract_rel_10 %>% filter(ZCTA5 == "20715") %>% select(1:5)
# A tibble: 8 x 5````
  ZCTA5 STATE COUNTY TRACT        GEOID
  <chr> <int> <chr>  <chr>        <dbl>
1 20715    24 033    800401 24033800401
2 20715    24 033    800402 24033800402
3 20715    24 033    800403 24033800403
4 20715    24 033    800409 24033800409
5 20715    24 033    800410 24033800410
6 20715    24 033    800504 24033800504
7 20715    24 033    800505 24033800505
8 20715    24 033    800513 24033800513

(NB: each of the 8 tracts within the 20715 ZIP Code, the state, county, and tract code are separated and then aggregated in the next column.)

PUMAs

PUMAs are Public Use Microdata Areas. According to the Census: PUMAs are a collection of counties or tracts within counties with more than 100,000 people. In practice, most of these places will more generous than the 100,000 allotment. For example, Nebraska (population 1.9 million) has eight-ish PUMAs. Isolating the PUMAs in the relationship file (see data table) will provide more information as to PUMA counts, but the easiest way to think of them is as regions or groups of smaller counties.

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