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 code schemes and geographic relationship files to properly control and present the data it collects for these important governmental units.

The boundaries of the primary governmental divisions of the United States, States, counties, and their statistical equivalents, generally are static and change only rarely; however, transfers of territory do occur from time to time. By contrast, the boundaries of incorporated places and even minor civil divisions are far more subject to change in most States.

Changes in State lines may result from legislation, court decisions, and other types of governmental action; changes in county boundaries are a matter of State law. Such boundary changes also may stem from more exact geographic descriptions, better maps, and improved surveying techniques. State boundaries may change by mutual agreement of the two State legislatures, subject to approval by the Congress.

In recent years, most boundary changes for counties have been minor and have not involved substantial shifts of population or land area. The independent cities in Virginia constitute an exception because they occasionally annex territory, as do the incorporated places in many States. Because the territory annexed by a Virginia city no longer is part of the county in which it had been located, changes in the boundaries of these independent cities also affect the boundaries of the adjacent county or counties. In other States, changes to counties occur on a piecemeal basis.

The Census Bureau has established procedures and programs to identify changes in legal boundaries and to record when and where they occur. The Census Bureau’s Boundary and Annexation Survey (BAS), conducted at periodic intervals immediately before each decennial census, and annually since 1972, determines the location of the boundaries of most major legal entities in the United States. The principal function of the BAS is to collect and maintain information on the inventory, status, boundaries, States, Counties, Equivalent Entities4-13