Figure 10-4. Effect of County Boundary Changes on Census Tracts and BNAs
Any changes to a county or State boundary that occur after census block numbering result in one county losing part of a census tract/BNA and another county gaining part of a census tract/BNA. Example 1 above shows the boundaries of Bibb County and Pike County, and the boundaries of their respective census tracts/BNAs at the time the Census Bureau assigned the census block numbers. When the Census Bureau updated the county boundaries, Bibb County lost area to Pike County; Pike County gained parts of Census Tracts 2 and 3 as shown in Example 2.
After updating the county boundary, the Census Bureau renumbered the affected census tracts/BNAs by adding the special suffix to the census tracts that lost area. As shown in Example 3, the Census Bureau renumbered Census Tracts 2 and 3 in Bibb County, creating Census Tracts 2.98 and 3.98. The Census Bureau then assigned new census tract/BNA numbers in the county gaining territory, using numbers that fit within the numbering scheme of that county. In Example 3, Pike County gained Census Tracts 5603.98 and 5604.98.
