Chapter 10
Census Tracts and Block Numbering Areas
Census tracts are small, relatively permanent geographic entities within counties (or the statistical equivalents of counties) delineated by a committee of local data users. Generally, census tracts have between 2,500 and 8,000 residents and boundaries that follow visible features. When first established, census tracts are to be as homogeneous as possible with respect to population characteristics, economic status, and living conditions.
Block numbering areas (BNAs) are geographic entities similar to census tracts, and delineated in counties (or the statistical equivalents of counties) without census tracts. For the 1990 census, the difference between census tracts and BNAs generally was the type of organization doing the delineation. Local census statistical areas committees (CSACs), often working at the county level, delineated or reviewed census tracts. State agencies and American Indian tribal authorities, sometimes with extensive assistance from the Bureau of the Census, delineated BNAs.
The Census Bureau uses census tracts and BNAs to collect, organize, tabulate, and present the results of its decennial censuses. Both census tracts and BNAs are an important part of the Census Bureau’s geographic hierarchy (see Figures 2-1 and 2-3 in Chapter 2). For the 1990 decennial census, the Census Bureau recognized 50,690 census tracts in the United States and Puerto Rico, and 11,586 BNAs in the United States, Puerto Rico, and the Outlying Areas under U.S. jurisdiction. Six States (California, Connecticut, Delaware, Hawaii, New Jersey, and Rhode Island) and the District of Columbia are covered completely by census tracts.
The first recorded instances of the delineation of small geographic entities based on population, topography, and housing characteristics were the sanitary districts of a special vital statistics study associated with the 1890 census. The Census Office, predecessor of the Census Bureau, worked with local officials in a number of cities to delineate a network of small geographic areas.
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