The Census is broken down into several dozen geographical units, ranging from the esoteric (Traffic Analysis Zones and Urban Growth Areas) to the standard (States, Counties, Cities). The most important geographies, however, are generally:

• Census Blocks – The atom of the Census, used to create voting districts. There are more than 10 million.
• Census Tracts – Generally a neighborhood-level geography. There are roughly 80,000.
• Places – These are generally incorporated cities or towns, although the Census Bureau may approve some smaller “Census Designated Places.” There are more than 30,000.
• Counties – There are more than 3,100 counties and county-equivalents (boroughs, parishes, etc.)
• States – All 50, plus territories and the District of Columbia.

Other permutations include almost 40,000 county subdivisions, which largely correlate to towns and villages in the Northeastern U.S.; metropolitan and micropolitan statistical areas; school districts; legislative districts (state and federal); zip code tabulation areas or ZCTAs that approximate the boundaries of a postal delivery area; and lands occupied by Native Americans, Alaskans, or Pacific Islanders.

Author: Frank Bass