# Census Block A **census block** is the smallest piece of ground the Census Bureau tabulates data for. Blocks are bounded by visible features such as streets, streams and railroad tracks, and by invisible ones such as city limits and property lines, and the Bureau's own materials describe them as nesting "within all other types of geographic areas" — which is what makes the block the building unit for everything that does not fit the standard hierarchy. Urban areas are delineated as cores of blocks; ZIP Code Tabulation Area boundaries are block boundaries; redistricting data is delivered by block under [[Public Law 94-171]]. The block is also the one level with no population rule attached to it. Census tracts and block groups both carry minimum and maximum population thresholds set by notice in the *Federal Register*; blocks carry none, because a block is too small to publish survey data for at all. The Bureau states plainly that it "does not publish ACS data for blocks." A block therefore has current numbers only in the year of a decennial census, and is dark for the rest of the decade — while remaining the unit at which legislative districts are drawn. > [!note] Stub > This is a short entry that hasn't been fully written yet. ## See also - [[Census Geography Tree]] — where the block sits, and the publication ladder that ends above it - [[Census]] · [[Public Law 94-171]] · [[Voting District]] · [[Block Boundary Suggestion Project]] - [[How a Redistricting Map Is Drawn and Challenged]] · [[Gerrymandering]]