HouseKnow

Where the data comes from

Every figure in a HouseKnow report comes from one of the datasets below. Nothing is estimated, interpolated, or bought from a commercial data broker.

The rules

If it is not in one of these sources, it is not in the report. A value we cannot verify is left out, not estimated and not shown as a dash that reads like a zero.

Every finding names its source and its date. Open any finding in a report and you get the agency, the dataset, the value the source returned, and when we asked.

Every finding names the area it describes. A flood zone read at the address and a hazard rating for a whole county are different kinds of fact, and the report keeps them apart.

Unavailable is reported as unavailable. Never as low, minimal, safe or none.

What we check, and what publishes it

Geographic precision is the important column. It says whether a result describes this location or the area around it.

Section Source Dataset Describes
Address resolution U.S. Census Bureau Geocoding Services API Documentation Census block
Flood FEMA National Flood Hazard Layer Documentation This location
Natural hazards FEMA National Risk Index Documentation Census tract
Wildfire USDA Forest Service Wildfire Hazard Potential, 2023 edition Documentation Region
Earthquake USGS National Seismic Hazard Model and earthquake catalog Documentation This location
Environmental EPA Facility Registry Service Documentation This location
Radon EPA Map of Radon Zones (1993) Documentation County
Disaster history FEMA OpenFEMA Disaster Declarations Summaries Documentation County
Wetlands U.S. Fish and Wildlife Service National Wetlands Inventory Documentation This location
Soil USDA NRCS Soil Survey Geographic Database (SSURGO) Documentation This location
Land and terrain USGS 3D Elevation Program (3DEP) Documentation This location
Area context U.S. Census Bureau American Community Survey 5-year estimates (2020 to 2024) Documentation Census tract
Market context FHFA House Price Index, all-transactions Documentation Metro area

Known limits

Coverage is not uniform. FEMA has not published a digital flood map for every county; downtown Midland, Texas, a city of 135,000 people, has none. The National Risk Index is not published for the U.S. territories. The Forest Service wildfire model covers the 50 states but not Puerto Rico, the U.S. Virgin Islands or Guam. Where a source does not cover a location, the report says so.

Addresses are located along the street, not on the building. The Census geocoder interpolates a position from the address ranges it holds for a street segment. Measured against five real addresses, the result sat between 200 and 770 metres from the building. Anything read at a coordinate inherits that, and the report says so on every report.

Maps can be old. A FEMA flood map is a formal publication that is revised infrequently: several of the addresses we tested are governed by panels that took effect in 2009. The EPA radon map dates from 1993 and has never been revised. Those dates are in the report because they matter.

Facility counts are a reporting artefact. The EPA facility registry holds millions of records, most of them small businesses complying with a disclosure rule. A California address appears to have four times as many nearby "regulated sites" as a Texas one, because California feeds more state programmes into the registry. HouseKnow therefore never headlines a raw count and never compares one state to another.

We do not offer deeds, liens, permits or ownership. Those are county records in thousands of separate systems. Promising them nationwide would mean guessing somewhere.

Attribution

This product uses the Federal Emergency Management Agency's OpenFEMA API, but is not endorsed by FEMA. The Federal Government or FEMA cannot vouch for the data or analyses derived from these data after the data have been retrieved from the Agency's website.

Wildfire data: USDA Forest Service, Wildfire Hazard Potential for the United States (270-m), version 2023, 4th Edition, Forest Service Research Data Archive. Flood mapping: FEMA National Flood Hazard Layer; the hardcopy FIRM and the accompanying study remain the official designation of special flood hazard areas. Geocoding by the U.S. Census Bureau.

HouseKnow is independent. FEMA, the EPA, the USGS, the USDA, the U.S. Fish and Wildlife Service, the FHFA and the U.S. Census Bureau do not endorse, certify or vouch for it.

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