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 Political/statistical area description (PSAD) A two-digit numeric code identifying each type of geographic entity in terms of its legal status or status as a statistical entity. (The Census Bureau established 98 PSADs for use in the 1990 census.) The Census Bureau uses PSADs to tabulate data for geographic entities by type, and, where necessary, to append the type to the entity name in the census data presentations.

Population density A numerical method of expressing the extent to which people are clustered within a specific geographic area, usually in terms of people per square mile or per square kilometer. The population density of an area is derived by dividing the total population of the entity by the total land area of the entity. See also jump, nonresidential urban land use, urban fringe, urbanized area.

Post office box address An address that refers to a box number in a post office building, and not to the actual physical location of a housing unit or business establishment. See also address, city-style address, general delivery address, rural address.

Precinct A legal entity subdividing a county, established by counties or municipalities for administrative or electoral purposes and used by the Census Bureau as an MCD in Illinois and Nebraska; one of several types of small geographic entities created by State and local governments for the purpose of administering elections, and for which the Census Bureau tabulated data in 1980 and 1990 as prescribed by Public Law 94-171. See also administrative entity, election precinct, minor civil division, voting district.

Primary metropolitan statistical area (PMSA) A geographic entity defined by the Federal OMB for use by Federal statistical agencies. If an area meets the requirements to qualify as a metropolitan statistical area (MSA) and has a population of one million or more, two or more PMSAs may be defined within it if statistical criteria are met and local opinion is in favor. A PMSA consists of a large urbanized county, or a cluster of such counties (cities and towns in New England) that have substantial commuting interchange. GlossaryG-39