Boundary and Annexation Survey (BAS)
Accurate boundaries are essential for accurate population counts. The Census Bureau's Boundary and Annexation Survey (BAS) updates:
- The nation's inventory of counties, townships (also called minor civil divisions, or MCDs), and incorporated places every year
- Legal boundaries, names and descriptions of each entity, and the geographic relationships between different legal areas.
The county BAS is the most important source for obtaining a complete inventory of municipalities and legal administrative units in the United States. The county BAS includes all counties in the U.S.every year. Participants are asked to review the:
- Boundaries of their counties
- Lists of all the known legal minor civil divisions and incorporated places within their counties
Minor Civil Division (MCD) BAS
The minor civil division (MCD) BAS is conducted only in states where townships are governments. Although Iowa's townships are legal administrative areas, they are not active governments under the Census Bureau's definition. The MCD BAS does not include Iowa.
The place BAS rotates the incorporated places surveyed each year:
- In years ending in 1,3,4,5,and 6, the BAS includes only incorporated places with a populations of 5,000 or greater.
- In years ending in 2 and 7 the population threshold is lowered to 2,500.
- In the three years before the decennial census, all incorporated places are included in the BAS regardless of size.
- In any BAS year, the Census Bureau will include some special areas, such as any newly incorporated places, places which have had an unusual change, or places needed for a special Census Bureau operation scheduled for that year.
For more information: