geoprimitives

Give it a longitude and latitude inside the United States and it answers with the Census FIPS codes for that point: the 2-digit state code, the 5-digit county GEOID, and the GEOID of the congressional district. Parameters go in the query string: this is a GET, there is no body. The codes are the product and the names are a courtesy. A county GEOID is the join key to essentially every geography-keyed federal dataset -- the American Community Survey, BLS Local Area Unemployment Statistics, BEA regional accounts, CDC WONDER, HUD, USDA, FEMA -- and the state code is its first two digits, so one call gives you both keys already in the form those tables expect. County GEOID is also the first five digits of a tract GEOID (11 digits) and of a block group GEOID (12), so it is the prefix you would filter a tract-level extract down with. COVERAGE, stated up front because the shortfall is the point: this endpoint answers state, county and congressional district, and it does NOT answer tract, block group, place or ZCTA. That is a size limit, not an oversight, and it was measured rather than guessed. A national compacted H3 index of tracts is 3196 KiB gzipped and of block groups 5335 KiB, at a resolution already too coarse for either; the whole Worker has 3 MiB compressed to spend and most of that was gone before this route existed. Those four tiers need an object store behind the Worker and will arrive with one. Every response repeats this under `coverage`, so an agent never has to infer it from a missing field. In the meantime geocoding.geo.census.gov answers all seven tiers, free, authoritative, at the cost of a round trip and a dependency. VINTAGE: TIGER/Line 2025, congressional districts for the 119th Congress. It is on every response under `vintage` and it matters more here than almost anywhere else in this catalog, because TIGER is re-cut annually and districts move with redistricting, so a stale district code is a wrong answer a caller cannot detect from the outside. Nothing here self-updates; a new vintage means a rebuild. The data is a work of the United States government and is in the public domain (17 U.S.C. 105) -- no attribution clause and no redistribution terms. ACCURACY, and this is the part to read before you trust a code. The boundaries themselves are full-resolution TIGER, the same geometry the Census Geocoder answers from, not a simplified copy. What is approximate is the lookup: the polygons are indexed as compacted H3 cells at resolution 7, about 1.22 km across, so a point within roughly 610 m of a boundary may be attributed to the neighbour. County equivalents and districts too small to describe at that resolution -- Falls Church city, the other Virginia independent cities, the congressional districts inside New York City -- carry a second index at resolution 9, about 87 m, and `boundaryAccuracyMetres` says which one answered you. Because a 610 m index is only useful if you know when not to trust it, every response carries `boundaryUnce