American Community Survey (ACS)

The Census Bureau has several tools to help you identify geographic boundary changes.

TIGER/Line shapefiles allow you to select a specific geographic area and vintage. You can overlay two different vintages within the GIS environment to visually or spatially detect any boundary changes between years. While shapefiles are the most flexible and comprehensive resource available, they are recommended only for experienced users of GIS software.

TIGER/Line shapefiles

The Census Bureau conducts the Boundary and Annexation Survey (BAS) annually to collect information about selected legally defined geographic areas. The BAS is used to update information about the legal boundaries and names of all governmental units in the United States. These legally defined geographic areas include counties and equivalent areas, minor civil divisions, incorporated places, American Indian reservations and American Indian off-reservation trust lands.

BAS publishes entity-based PDF maps of updated legal boundaries. BAS maps are only available for the current and previous BAS year. The 2012 and 2013 BAS maps are currently available. The BAS maps display the updated legal boundaries and names valid thru January 1, for all governmental units that participated in that year's BAS. For example, the 2012 BAS maps display the updated legal boundaries and names valid thru January 1, 2011, for all governmental units that participated in the 2011 BAS. These legal entities include counties or county equivalents, minor civil divisions (MCDs; county subdivisions that are legal areas in 29 states), places, consolidated cities, American Indian areas/Alaska Native areas (AIAs) and Hawaiian Home Lands (HHLs).

Boundary and Annexation Survey Maps

American FactFinder (AFF) has an internet mapping application. To compare boundary vintages on AFF, click Geographies on the left navigation. An overlay window will appear. Select the desired geographic area by using the name search or filter options in the left navigation. Next click on the Map tab in the Geography overlay. The map will display the latest boundary vintage in yellow. To make comparisons, select a different boundary vintage using the Boundaries and Features tab on the left.

The Boundaries and Features tab allows you to select geographic vintages by using the dropdown box labeled Display Boundaries and Features from. Some boundaries are only available in certain vintage years. For example, census block groups are found in the 2012, 2011, 2010 and 2000 boundary vintages, but do not appear in the other vintage years. Places can be selected from each boundary vintage, because incorporated places do have the potential to change each year. AFF is missing vintages for 2001 and 2003.

The Geographic Boundary Change Notes provide a list of changes to incorporated places, census designated places, consolidated cities, county subdivisions, counties and equivalent areas, and American Indian, Alaska Native, and Native Hawaiian areas.

Types of changes found on this website include:

• new entities;
• dissolution of entities;
• changes in higher-level geographic relationships (state, county, and county subdivision levels);
• mergers or consolidations of two or more entities;
• name changes and corrections;
• legal or statistical area description changes;
• functional status changes;
• changes in status of incorporated places as either dependent within or independent of surrounding county subdivisions;
• county redistricting;
• census code changes and corrections; and
• Federal Information Processing Series (FIPS) code changes and corrections.

The Geographic Boundary Change Notes only include boundary change information for existing legal areas that resulted in changes to hierarchical relationships with other geographic areas, and do not include information on all annexations. For example, if an incorporated place annexes unincorporated territory within the same county, then a change note is not recorded. However, if an incorporated place annexes unincorporated territory in a neighboring county, then a change note is recorded for the first annexation that resulted in a relationship change. Any additional annexations into the neighboring county will not be recorded, because the geographic area relationship is not changing as a result of the subsequent annexations.

The Geographic Boundary Change Notes are not recommended for identifying annexations for legal areas. The change notes do not include comprehensive information about 2010 Census changes to census designated places (CDPs). We recommend visiting the Geographic Comparability File - 2010 to 2000 Places to understand changes affecting 2010 CDPs.

Geographic Boundary Change Notes