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 to tabulate the results of its decennial censuses. This enabled the Census Bureau to avoid last-minute updates and revisions of boundaries and to put its efforts into field enumeration, processing of results, and preparation for data tabulations—all under extremely stringent time constraints.

Annexation is the legal expansion of corporate limits. It commonly involves the transfer of territory outside the jurisdiction of any municipal-type government into an incorporated place, but it also may involve a transfer of land between two or more incorporated places. In the Northeastern States and parts of the Midwest, annexations by some incorporated places transfer land between governmental entities (from the jurisdiction of MCDs to places). Detachment is the reverse of annexation, whereby an incorporated place relinquishes territory to another jurisdiction. Detachments occur considerably less frequently than do annexations.

Annexation practices vary greatly among the States. In some States, incorporated places merely file ordinances and immediately take over new territory; in others, there are annexation elections involving voters of both the annexing place and the territory proposed for annexation. Still other States establish a period of time over which the municipal government bringing the boundary change action must demonstrate that it can supply or improve upon the governmental services existing in the territory proposed for annexation. In some States, annexation or detachment actions do not become effective until a specified time after enactment. Differing State laws, intergovernmental relationships, political power balances, historic settlement patterns, and customary practices resulted in variations by State in the percentage of incorporated place boundary changes in the 1980 to 1990 period from zero in most of the New England States to over 80 percent in California (see ).

Mergers represent the combination of two or more governmental units into one. They usually involve like governments, most often incorporated places, but occasionally represent the combination of an incorporated Places9-15