The Boundary and Annexation Survey (BAS) and the Block Boundary Suggestion Project (BBSP) are often conflated; both involve local geography and the Census Bureau, but they do different jobs. BAS is the Bureau’s annual survey to keep the legal boundaries and names of governments current, such as city limits, county lines, township boundaries, and tribal areas. BBSP is a once-a-decade phase of the Redistricting Data Program in which a state suggests which features the Bureau should use as statistical census tabulation block (census block) boundaries.
The other differences follow from that split. BAS runs every year, and each eligible government submits its own boundary updates directly to the Census Bureau. BBSP runs on a decennial cycle and is submitted through the state’s nonpartisan Redistricting Data Program liaison rather than by individual governments, so local officials participate by working through that liaison. Their purposes differ as well; BAS keeps legal boundaries accurate so the census assigns population to the right jurisdiction, while BBSP shapes where census block lines fall so they align with the features that define precincts.
The two programs are complementary. In the Bureau’s MAF/TIGER database, a single feature can serve as several kinds of boundaries at once; a road can be both a block boundary and a place (legal) boundary, so the legal boundaries kept current through BAS are already reflected in the block geography (see figure below).
BBSP then handles the non-legal features: power lines, ridgelines, property lines, etc., that define precincts but would not otherwise become block edges. The takeaway for a local office is to treat them as a pair, respond to BAS each year to keep legal boundaries in order, and work with your state liaison on BBSP to get the electoral features captured.
For more, see the Census Bureau’s Boundary and Annexation Survey page and its Redistricting Data Program Management page.
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