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 collection block number; census blocks that nest entirely within collection blocks are not suffixed. A census block is always unique to, and can never cross the boundaries of, either a census tract or a BNA. All standard geographic tabulation entities are made up of whole tabulation blocks.

State and county boundaries form the framework within which the Census Bureau numbers census tracts and BNAs; thus, census blocks never cross these boundaries. In the rare instances where a State or county boundary change is reported after census tract/BNA numbers are entered, the Census Bureau assigns suffixes to the census block numbers for data tabulation.

County subdivisions include census county divisions (CCDs) and minor civil divisions (MCDs). CCD boundaries usually do not split census blocks. This is because they generally follow physical features that normally are held as census tract/BNA boundaries. On the other hand, many MCD boundaries do not follow physical features; thus, they frequently split census collection blocks, except in certain States (Connecticut, Maine, Michigan, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Wisconsin) where they are more stable and often held as census tract/BNA boundaries.

As with MCDs, many incorporated place boundaries do not follow physical features; as a result, they usually split census collection blocks. (An exception often is made when the boundary of an incorporated place is conjoint with the boundary of another incorporated place; in these cases, the Census Bureau allows the place boundary to also be a census tract/BNA boundary.) In some States (Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont), most incorporated place boundaries also coincide with MCD lines. These lines are stable in these States, and are held as census block boundaries. Census designated place (CDP) boundaries usually are defined to follow physical features. Therefore, many of their boundaries also are census collection block boundaries. Since Census Blocks and Block Groups11-17