Contextual Data Archive (CDA) Data Set No. B1-B4

Census Tracts/BNAs, 1970, 1980, & 1990

Census Tracts and BNAs are small, relatively permanent statistical subdivisions of a county. Census tracts are delineated for all metropolitan areas and other densely populated counties by local census statistical areas committees following Census Bureau guidelines. Census tracts usually have between 2,500 and 8,000 persons and when first delineated, were designed to be homogeneous with respect to population and characteristics, economic status, and living conditions. Census tracts do not cross state or county boundaries. In all but a very small number of cases in New England, census tracts do not cross metropolitan area boundaries.

Census tracts are the basic statistical reporting unit in metropolitan areas: block numbering areas (or BNAs) are analogues to census tracts in non-metropolitan area counties and remote rural areas. It is an area that has been "blocked" by the census but is not tracted, and the Census Bureau in most respects treats the tract and BNA data as a single level of aggregation. BNAs are drawn using guidelines similar to those for the delineation of census tracts. As with census tracts, BNAs do not cross county or state boundaries.

Data set B1-B4 of the Contextual Data Archive includes socio-economic and demographic data for all census tracts/BNAs in the US. B1 consists of data from the 1970 Census, and has 36,312 cases and 680 variables. B2 covers data from the 1980 Census, and includes 878 variables for 46,520 cases. B3-B4 covers data from the 1990 Census and includes 1,021 variables for 61,258 cases.

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