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GIS Web Services for the FEMA National Flood Hazard Layer (NFHL)

Due to a recent change in security settings, some clients are experiencing difficulties using https links. We recommend using http links when referencing the NFHL GIS services, ie. http://hazards.fema.gov/gis/nfhl/rest/services.

FEMA’s National Flood Hazard Layer

FEMA provides access to the National Flood Hazard Layer through web mapping services. The National Flood Hazard Layer is a computer database that contains FEMA’s flood hazard map data.

The data depict flood hazard information and supporting data used to develop the information. The primary flood hazard classification is indicated in the Flood Hazard Zones layer.

The NFHL layers include:

  • Flood hazard zones and labels
  • River Miles Markers
  • Cross-sections and coastal transects and their labels
  • Letter of Map Revision (LOMR) boundaries and case numbers
  • Flood Insurance Rate Map (FIRM) boundaries, labels and effective dates
  • Coastal Barrier Resources System (CBRS) and Otherwise Protected Area (OPA) units
  • Community boundaries and names
  • Levees
  • Hydraulic and flood control structures
  • Profile and coastal transect baselines
  • Limit of Moderate Wave Action(LiMWA)

Not all effective Flood Insurance Rate Maps (FIRM) have GIS data available. To view a list of available county and single-jurisdiction flood study data in GIS format and check the status of the NFHL GIS services please visit the NFHL Status Page.

FEMA GeoPlatform

The NFHL GIS service is available through FEMAs GeoPlatform, an ArcGIS Online portal containing a variety of FEMA-related data.

To view the NFHL on the FEMA GeoPlatform go to NFHL on FEMA GeoPlatform.

Technical Information

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, ensure that the other information meets FEMA’s standards for map accuracy.

The minimum horizontal positional accuracy for base map hydrographic and transportation features used with the NFHL is the NSSDA radial accuracy of 38 feet. USGS imagery and map services that meet this standard can be found by visiting the Knowledge Sharing Site (KSS) for Base Map Standards (420). Other base map standards can be found at https://riskmapportal.msc.fema.gov/kss/MapChanges/default.aspx. You will need a username and password to access this information.

The NFHL data are from FEMA’s Flood Insurance Rate Map (FIRM) databases. New data are added continually. The NFHL also contains map changes to FIRM data made by Letters of Map Revision (LOMRs).

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 & 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 maps at map scales of 1:50,000 and larger. The "Scalehint" item in the Capabilities file for the Web Map Service encodes the scale range for a layer.

In addition, there are non-NFHL datasets provided in 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-Fs). The Letters of Map Amendment (LOMA) are positioned less accurately than are the National Flood Hazard Layer data.

Layers in the public NFHL GIS services:

Use the numbers shown below when referencing layers by number.

      0. NFHL Availability
      1. LOMRs
      2. LOMAs
      3. FIRM Panels
      4. Base Index
      5. PLSS
      6. Toplogical Low Confidence Areas
      7. River Mile Markers
      8. Datum Conversion Points
      9. Coastal Gages
      10. Gages
      11. Nodes
      12. High Water Marks
      13. Station Start Points
      14. Cross-Sections
      15. Coastal Transects
      16. Base Flood Elevations
      17. Profile Baselines
      18. Transect Baselines
      19. Limit of Moderate Wave Action
      20. Water Lines
      21. Coastal Barrier Resources System Area
      22. Political Jurisdictions
      23. Levees
      24. General Structures
      25. Primary Frontal Dunes
      26. Hydrologic Reaches
      27. Flood Hazard Boundaries
      28. Flood Hazard Zones
      29. Submittal Information
      30. Alluvial Fans
      31. Subbasins
      32. Water Areas

GIS Web Services Information

For users experienced with GIS, a variety of services are offered for the public to access NFHL data. The services contain predefined symbology similar to the printed FIRM panels onto which the data is mapped. Though the services contain all NFHL spatial layers, some are only available in certain scale ranges; for instance, detailed flood maps are only available when zoomed past 1:50,000 scale.

ArcGIS REST Service

The ArcGIS REST service provides direct access to NFHL spatial information through ESRI applications such as ArcGIS Desktop or ArcGIS Online. This service supports mapping, data, and query requests.

To access the public NFHL service directly through a web map viewer such as ArcGIS Online, you can use the service-specific URL. Copy & Paste the following URL into your web map viewer:

http://hazards.fema.gov/gis/nfhl/rest/services/public/NFHL/MapServer

Note: Clicking on this URL and opening it in your browser will return an error. It is intended to be used within a web map viewer.

To access the service through a client like ArcGIS Desktop, you can use the service directory URL:

http://hazards.fema.gov/gis/nfhl/services

Then select the "public" folder and navigate to the "NFHL" service.

OGC Web Mapping Service (WMS)

Use the following URL in your GIS Application:

http://hazards.fema.gov/gis/nfhl/services/public/NFHLWMS/MapServer/WMSServer

The WMS Capabilities file is available here:

http://hazards.fema.gov/gis/nfhl/services/public/NFHLWMS/MapServer/WMSServer?request=GetCapabilities&service=WMS

The NFHL Web Mapping Service provides an OGC-compliant protocol for obtaining map images and querying feature information. This service can be consumed by a number of free and commercial GIS clients.

OGC Web Feature Service (WFS)

Use the following URL in your GIS Application:

http://hazards.fema.gov/gis/nfhl

/services/public/NFHL/MapServer/WFSServer

The NFHL Web Feature Service provides an OGC-compliant protocol for direct download of GIS data from the NFHL. This service can be consumed by a number of free and commercial GIS clients. Requests are currently limits to 1000 features, so it is recommended that users focus on a very limited area of interest when requesting data through WFS. If a larger amount of data is needed, it is recommended that users download the NFHL data by state or county from the MSC.

Due to limitations on the number of features that can be requested, it is recommended that users supply bounding box coordinates when constructing WFS requests. Here is an example of a WFS GetFeature request for the Flood Hazard Zone layer.

For more information on constructing WFS requests, see the topic on the ESRI help site.

If you have any questions or concerns please contact MIP Help (miphelp@riskmapcds.com ) or the FEMA Map Information eXchange (FMIX) at 1-877-FEMA-MAP