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2012 BAS Map Files Description Page

The U.S. 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 governmental units in the United States.  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.  The BAS maps are created for the following entity types:

The BAS entities are displayed on three different types of mapsheets:  Index, Inset, and Parent.  Index sheets show the entire entity boundary for entities that are too large to be printed on one single mapsheet.  In addition, index mapsheets also show the total number of mapsheets for that particular entity, and any inset sheets in an entity.  Index maps are assigned a mapsheet number of ‘000’.  Inset mapsheets show a larger view for areas that are too small to view in the standard parent mapsheet.  An example of an inset mapsheet number is ‘A01’.  Parent mapsheets show a portion of an entity boundary, or the entire entity boundary for those entities that are small enough to be printed on one single mapsheet.  An example of a parent mapsheet number is ‘003’.

NOTE:   Some of the maps are very large in size and downloading time for these maps will vary depending on your internet access speed.

Source: U.S. Census Bureau
Geography Division
Geographic Areas Branch