The National Flood Hazard Layer (NFHL) is a digital database that contains flood hazard mapping data from FEMA’s National Flood Insurance Program (NFIP). This map data is derived from Flood Insurance Rate Map (FIRM) databases and Letters of Map Revision (LOMRs).The NFHL is for community officials and members looking to view effective regulatory flood hazard information in a Geographic Information Systems (GIS) application.
The NFHL provides users with the ability to determine the flood zone, base flood elevation and floodway status for a particular geographic location. It also has National Flood Insurance Program (NFIP) community information, map panel information, cross section and hydraulic structure information, Coastal Barrier Resource System information (if applicable) and base map information, such as road, stream and public land survey data. A full list of the layers available in the NFHL may be found in the NFHL GIS Services User Guide.
The NFHL dataset represents the current effective flood risk data for those parts of the country where maps have been modernized. It is a compilation of effective Flood Insurance Rate Map (FIRM) databases and Letters of Map Revision (LOMR). The NFHL is updated as new data reaches its designated effective date and becomes valid for regulatory use under the NFIP.
Accessing the NFHL
You may view and download NFHL data online using the FEMA GeoPortal or by downloading a KMZ file, which overlays the data in Google Earth ™. A series of dedicated GIS web services allow the NFHL to be incorporated into websites and GIS applications. Additionally, NFHL data is available for download from the FEMA Flood Map Service Center and can be added to most GIS applications normally used to perform spatial analyses. Once accessed, the data can be integrated into custom maps and reports. To do so, you will need GIS or mapping software that can read data in shapefile format or incorporate one of the web services mentioned above.
Using the NFHL to Make Official Determinations
Per FEMA regulations, flood hazard and supporting data are developed using specifications for horizontal control consistent with 1:12,000–scale mapping. If you plan to display maps from the National Flood Hazard Layer with other map data for official purposes, please ensure that the other information meets FEMA’s standards for map accuracy. U.S. Geological Survey (USGS) base map data and services are available that meet this standard.
The NFHL is stored in North American Datum of 1983, Geodetic Reference System 80 coordinate system, though many of the NFHL GIS web services support the Web Mercator Sphere projection commonly used in web mapping applications.
Organization and Display
The NFHL is organized into many data layers. The layers display information at map scales appropriate for the data. A layer indicating the availability of NFHL data is displayed at map scales smaller than 1:250,000, regional overviews at map scales between 1:250,000 and 1:50,000 and detailed flood hazard data at map scales of 1:50,000 and larger.
There are also several non-NFHL datasets provided through the GIS web services, such as information about the availability of flood data and maps, the national map panel scheme and point locations for Letters of Map Amendment (LOMA) and Letters of Map Revision Based on Fill (LOMR-F). The items on the LOMA Point Layer are positioned less accurately than the NFHL data due to limitations on the precision of the geographic points associated with each LOMA. The individual letters themselves contain more precise location information.
Relevant Links to the NFHL
FEMA GeoPlatform: the NFHL is made available for viewing on the FEMA GeoPlatform and coupled with a USGS base map service that meets FEMA specifications for accuracy. This online map viewer may be used for official NFIP purposes.
NFHL Status Page: provides the current status of NFHL services and data. The Announcements section provides information about maintenance windows and new information. The NFHL Inventory Table provides the user with an updated list of databases in the NFHL, sortable by state, county, date updated and ID.
GIS Web Services for the FEMA National Flood Hazard Layer (NFHL): visit this page for information regarding the various GIS Services available to access the NFHL. This information includes extended services geared towards experienced GIS users.
Using the National Flood Hazard Layer Web Map Service (WMS) in Google EarthTM: visit this page to learn about how to use the NFHL in the Google EarthTM application, including information on how to download Google EarthTM onto your computer and how to download the NFHL or Stay Dry KMZ files.