Platform · Glossary
Block group.
A Census geography one level below the tract, typically 600 to 3,000 residents. Tracts contain anywhere from one to about a dozen block groups depending on density.
When block group is the right resolution
For most ACS variables, the block group is the finest published geography. If you're trying to understand income or rent variation inside a single tract — say, a tract that straddles a freeway with very different neighborhoods on either side — block group is the lens that resolves it.
When 3Y uses block groups vs. tracts
Most 3Y market pages aggregate to the census tract because tract-level data is more stable across releases and supports cleaner comparison across cities. Block group data can show up in property-level analyses where the radius is small enough that a single tract is too coarse — for example, when computing local benchmarks on a property in a dense urban core.