Page:Geographic Areas Reference Manual (GARM).pdf/274

 In most instances, the census collection block is identical to the tabulation block. The difference arises where the boundary of a higher-level geographic entity, such as an incorporated place or an MCD, splits a collection block. In such instances, the Census Bureau adds an alphabetic suffix to the collection block number, thereby uniquely identifying each piece of tabulation geography located within the census collection block. This methodology permits the Census Bureau to accommodate changes to the boundaries of legally recognized entities as they occur and still maintain a stable inventory of collection blocks. It also corrects a source of great confusion that occurred during earlier block number presentations in which all portions of the collection block had the same block number and the data user had to search all other geographic entity codes to determine why data were presented for what appeared to be only a portion of the block.

Figure 11-3. Collection Blocks Split by a Geographic Entity Boundary After assigning alphabetic suffixes to all portions of the collection blocks intersected by another tabulation boundary, the Census Bureau refers to them as census tabulation blocks. (Not all tabulation blocks carry suffixes; in fact, most tabulation block numbers are identical to the collection block numbers.) Only where a collection block is split by a geographic boundary is a suffix added to the collection block number. In the example shown in 11-14Census Blocks and Block Groups