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 suffixed part representing a new block (see, “Census Blocks and Block Groups”). The boundaries of census tracts, BNAs, and block groups generally do not follow incorporated place boundaries because place boundaries are subject to frequent change, whereas census tracts and BNAs are designed to be essentially stable units for intercensal data comparisons (see, “Census Tracts and Block Numbering Areas”). An exception is the use of incorporated place boundaries as census tract, BNA, and block group boundaries in States of the Northeast; another exception occurs where there are conjoint (shared) boundaries between two incorporated places. Urbanized areas include whole CDPs, and generally include whole incorporated places except in the case of extended cities (see the “” section in this chapter).

At one time, places were the only geographic units the Census Bureau used for determining the urban and rural populations and areas of the United States. Before 1950, the Census Bureau classified incorporated places having 2,500 or more residents as urban; it classified all smaller incorporated places, together with nonplace territory, as rural. In addition to incorporated places, the Census Bureau designated certain densely settled MCDs as urban places. For 1950, the Census Bureau introduced urbanized areas (UAs) to better define large agglomerations of population (see, “The Urban and Rural Classifications”). It also introduced census designated places (CDPs), then known as unincorporated places. These two measures provided a better classification of densely developed area outside of incorporated places.

Incorporated places vary greatly in population, in physical extent, in the stability of their boundaries, and in their usefulness as a measure of the urban population of an area. The largest incorporated place in the Nation has more than seven million inhabitants, the smallest, fewer than ten. The largest incorporated place, in areal measure, has more than 2,800 square miles; the smallest, a few acres. ( lists the places that encompass more than 100 square miles of land.) Places9-11