2020 Census Block Assignment and Redistricting Files (tract-to-place)
Census files that record which places each census block belongs to, used to relate tracts and the cities and towns they sit in.
Census tracts and incorporated places are two different ways of dividing the country, and neither nests inside the other: a city can contain many tracts, and a tract can straddle a city line or lie outside any city at all. The Bureau publishes Block Assignment Files, which "contain Census tabulation block codes and geographic area codes for a specific geographic entity type," alongside the 2020 redistricting summary file, which reports population and housing counts for the same blocks. Read together, they record how tracts and places overlap.
Coverage#
The 2020 vintage covers the 50 states and the District of Columbia. Across the universe we hold, 85,395 tracts relate to 31,909 places through 153,074 distinct tract-place overlaps. Blocks falling outside any incorporated place or census designated place are recorded as unassigned rather than dropped.
How we use it#
This is reference geography. It establishes which cities and towns a given tract belongs to, and how completely, so that information published for a place can be associated with the tracts inside it and vice versa. Several measures published for cities and towns reach the tract map this way, including crime and building permits. No Birdseye metric reports these files as a value in their own right.
Considerations#
Overlaps vary enormously in quality. Some tracts sit entirely within one city; others are split across several jurisdictions or fall largely outside any place, and a place-level figure is a much weaker description of the second kind of tract than the first. We record that difference rather than treating every tract as equally well matched.
The files are decennial. Municipal boundaries change through annexation between censuses, so the relationship drifts from current legal boundaries as the decade goes on.
Citation#
U.S. Census Bureau, 2020 Census Block Assignment Files and 2020 Census Redistricting Data (P.L. 94-171) Summary File.
Per Census Bureau guidance, the Bureau is cited as the source of the original data only. Figures we derive from these files are our own.
References#
- 1US Census Bureauhttps://www.census.gov/geographies/reference-files/time-series/geo/block-assignment-files.html
- 2Census Bureau guidancehttps://www.census.gov/about/policies/citation.html