Geography

Geographic Terms and Concepts - Boundary Changes

Many of the legal and statistical entities for which the Census Bureau tabulates decennial census data have had boundary changes between Census 2000 and the 2010 Census; that is, between January 1, 2000, and January 1, 2010.  Boundary changes to legal entities result from:

1. Annexations to or detachments from legally established governmental units.
   
2. Mergers or consolidations of two or more governmental units.
   
3. Establishment of new governmental units.
   
4. Disincorporations or disorganizations of existing governmental units.
   
5. Changes in treaties or executive orders and governmental action placing additional lands in trust.
   
6. Decisions by federal, state, and local courts.
   
7. Redistricting for congressional districts and state legislative districts.
   
8. Ancillary changes to legal or statistical areas as a result of annexations and detachments; for example, reduction of territory for a census designated place as the result of an annexation by an adjacent incorporated place.
   
9. Changes to correct errors or more accurately place boundaries relative to visible features.
   
10. Changes to statistical areas as the result of concept or criteria changes.

All legal boundaries used for the 2010 Census are those reported to the Census Bureau to be in effect as of January 1, 2010.  The statistical area boundaries also reflect a January 1, 2010, date for delineation.  The legal boundaries are collected through various surveys and programs:  the Boundary and Annexation Survey, Redistricting Data Program, and the School District Review Program.  There is a Geographic Change User Note Indicator in data files that identifies entities for which there have been changes to boundaries or data attributes (for example, legal/statistical area description or code) between the two censuses.

Statistical entity boundaries generally are reviewed by local, state, or tribal governments and can have changes to adjust boundaries to visible features to better define the geographic area each encompasses or to account for shifts and changes in the population distribution within an area.  Where statistical areas have a relationship to legal area boundaries, complementary updates occur; for example, removing territory from a census designated place if annexed to an incorporated place or contracting a tribal designated statistical area if the area is added to an American Indian reservation.

The historical counts shown for states, counties, county subdivisions, places, American Indian, Alaska Native, and Native Hawaiian areas, and other areas are not updated for boundary changes and thus, reflect the population and housing units in each entity as delineated at the time of each decennial census.