FEMA National Flood Hazard Layer
FEMA
Flood zones, base flood elevations, and floodways for pre-disaster planning — 'is my home/route in a flood zone' is a headline offline feature for a survival app, and flooding is the most common US disaster.
Editor's notes
Not all counties have digital NFHL data (coverage gaps in rural areas). Data changes as LOMRs take effect — bundled extracts go stale; for insurance/legal determinations only the official FIRM governs, so include a disclaimer. Convert GDB to tiles/GeoPackage for mobile use.
Esri File Geodatabase: county/state extracts via the Map Service Center (msc.fema.gov 'Search All Products'), or the multi-part NFHL_National download; also live GIS web services
National GDB ~12 GB uncompressed; county extracts typically 10-500 MB
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Source & license
US federal government work (public domain).
Use of this material does not imply endorsement by its publisher or any government agency.