The Census Bureau conducts the Boundary and Annexation Survey (BAS) annually to collect information about selected legally defined geographic areas. The ACS uses legal boundaries as of January 1 of the last year of the estimate period, as reported to the Census Bureau.

Geographic Area	2012 Estimate Year
State and State Equivalent	January 1, 2012
County or equivalent (Alaska boroughs, Louisiana parishes, Puerto Rico municipios, independent cities)	January 1, 2012
County Subdivision
Minor Civil Division (MCD)/Barrio and Barrio-Pueblo	January 1, 2012
Place
Incorporated Place	January 1, 2012
American Indian/Alaska Native/Hawaiian Home Land
Alaska Native Regional Corporations (ANRCs)	2010 Census
Federal American Indian Reservation (federal AIR)	January 1, 2012
State American Indian Reservation (state AIR)	2010 Census
American Indian Tribal Subdivision, federal AIR	January 1, 2012
Hawaiian Home Land (HHL)	2010 Census
Other Legal Areas
Congressional District, Delegate District DC, Resident Commissioner District PR	January 1, 2013¹
School District (Elementary, Secondary, Unified)^*	2011-2012 January 1, 2012
Consolidated City	January 1, 2012

^*School district boundaries are updated every two years as part of the School District Review Program.

¹113th Congress of the United States

Statistical Areas

For statistical areas, boundary changes most often take place with each decennial census. Statistical areas are designed to have stable boundaries.

Geographic Area	2012 Estimate Year
County Equivalent (Census Areas in Alaska)	January 1, 2012
County Subdivision
Census County Division (CCD)	2010 Census
Place
Census Designated Place (CDP)/Zona Urbana and Comunidad	2010 Census
American Indian/Alaska Native/Hawaiian Home Land
Tribal Designated Statistical Area (TDSA)	2010 Census
State Designated Tribal Statistical Area (SDTSA)	2010 Census
Oklahoma Tribal Statistical Area (OTSA)	2010 Census
American Indian Tribal Subdivision, OTSA	2010 Census
Tribal Tract	2010 Census
Tribal Block Group	2010 Census
Alaska Native Village Statistical Area (ANVSA)	2010 Census
Other Statistical Areas
Metropolitan Statistical Area/Micropolitan Statistical Area	December 1, 2009
Metropolitan Statistical Area/Micropolitan Statistical Area - Principal City	December 1, 2009*
New England City and Town Area (NECTA)	December 1, 2009
New England City and Town Area - Principal city	December 1, 2009*
Urban Area	2010 Census
Census Tract	2010 Census
Census Block Group	2010 Census
Public Use Microdata Area (PUMA)	2010 Census
5-digit ZIP Code Tabulation Area (ZCTA)	2010 Census

^*While the American Community Survey (ACS) data generally reflect the Office of Management and Budget (OMB) definitions of metropolitan and micropolitan statistical areas; in certain instances the names, codes, and boundaries of the principal cities shown in ACS tables may differ from the OMB definitions due to differences in the effective dates of the geographic entities.