Data sources, methods and limits
Every number in an Aeonis Flood report comes from a public source, fetched live or cached for up to 30 days. Here is exactly how.
| Report item | Source | Licence / terms |
|---|---|---|
| Flood zone, base flood elevation, zone depth, nearby zones, map panel, community ID, LOMRs, LOMAs | FEMA National Flood Hazard Layer (NFHL), hazards.fema.gov ArcGIS services, queried at the pin | U.S. Government work, public domain |
| Flood insurance claims by ZIP code | FEMA OpenFEMA, NFIP Redacted Claims v3 | Public domain; OpenFEMA terms (no FEMA endorsement implied) |
| Disaster declarations by county | FEMA OpenFEMA, Disaster Declarations Summaries v2 | Public domain |
| NFIP participation and Community Rating System class | FEMA OpenFEMA, NFIP Community Status Book | Public domain |
| Ground elevation | USGS Elevation Point Query Service (3D Elevation Program), NAVD88 feet | Public domain |
| Datum conversion (NGVD29 to NAVD88) | NOAA VDatum API | Public domain |
| Address matching, county, ZIP code tabulation area | U.S. Census Bureau Geocoder | Public domain |
| Address suggestions and fallback matching | © OpenStreetMap contributors via Photon (Komoot) and Nominatim | ODbL 1.0, attribution required |
| Map library | Leaflet 1.9.4 | BSD 2-Clause |
| Basemap imagery | USGS The National Map (Imagery Topo) | Public domain |
How the report is built
- Zone at the pin. We query NFHL flood hazard polygons at the exact coordinates. If polygons overlap, we show the highest-risk one. We also search a radius of about 60 m (200 ft) and warn you if a higher-risk zone is that close.
- Base flood elevation. Taken from the zone polygon when FEMA publishes a single value. On rivers where it varies, we show the range of BFE lines within about 300 m.
- Ground vs. BFE. USGS bare-earth elevation at the pin minus the BFE. If the BFE uses the older NGVD29 datum, we convert it to NAVD88 with NOAA VDatum first. Ground elevation is not the elevation of the building's lowest floor.
- 30-year chance. A 1% annual chance compounds to about 26% over 30 years (1 − 0.99³⁰); 0.2% compounds to about 6%.
- Claims. All NFIP claims whose reported ZIP matches, up to the most recent 10,000 for the largest ZIPs (the total count is always exact). Amounts include building, contents and increased-cost-of-compliance payments, not adjusted for inflation.
- Disasters. Unique FEMA declarations (major disaster, emergency and fire management) designated for the county since January 1, 2000.
Usage limits we follow
Nominatim is only used as a fallback, at most about one request per second, with results cached; Photon address suggestions are cached and limited per network. FEMA, USGS, NOAA and Census services are free public APIs; we cache their results (up to 30 days) to limit load.
Limits
Address points can sit on the street rather than the building, so drag the pin onto the structure. NFHL coverage is incomplete in some counties, and preliminary maps that aren't yet effective are not shown. Data providers can be slow or down; when a section is missing the report says so. Reports are information only, not an official determination; see the Terms.
This product uses the FEMA OpenFEMA API and National Flood Hazard Layer, 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(s). FEMA, USGS, NOAA and the Census Bureau do not endorse Aeonis Flood.