GIS Web Services for the FEMA National Flood Hazard Layer (NFHL)
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FEMAs National Flood Hazard Layer
FEMA provides access to the National Flood Hazard Layer (NFHL) through web mapping services. The NFHL is a computer database that contains FEMA�s flood hazard map data. The simplest way for you to access the flood hazard data, including the NFHL, is through FEMAs Map Service Center (MSC). If you want to explore the current digital effective flood hazard data in a map, the best tool to use is the NFHL Viewer. From the NFHL Viewer, you may view, download, and print flood maps for your location
The data depict effective 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
- 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 geographic information system (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.
Preliminary & Pending National Flood Hazard Layers
The Preliminary and Pending NFHL dataset represents the current pre-effective flood data for the country. These layers are updated as new preliminary and pending data becomes available, and data is removed from these layers as it becomes effective.
Preliminary & Pending Data
Preliminary data are for review and guidance purposes only. By viewing preliminary data and maps, the user acknowledges that the information provided is preliminary and subject to change. Preliminary data are not final and are presented in this national layer as the best information available at this time. Additionally, preliminary data cannot be used to rate flood insurance policies or enforce the Federal mandatory purchase requirement. FEMA will remove preliminary data once pending data are available. The preliminary flood hazard data is available through the preliminary FEMA Map Products page. If the preliminary flood hazard data search tool is unavailable, please use the alternate site. To explore the current digital preliminary flood hazard data in a map, the best tool to use is the Flood Map Changes Viewer (FMCV). From the Flood Map Changes Viewer, you may view, download, and print flood maps for your location.
Pending data are for early awareness of upcoming changes to regulatory flood map information. Until the data becomes effective, when it will appear in FEMA's National Flood Hazard Layer (NFHL), the data should not be used to rate flood insurance policies or enforce the Federal mandatory purchase requirement. FEMA will remove pending data once effective data are available.
To better understand preliminary data please see the Preliminary National Flood Hazard Layer webpage.
FEMA's GIS flood map services are 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.
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 NFHL with other map data for official purposes, ensure that the other information meets FEMAs 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.
United States Geological Survey (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 FEMAs FIRM databases.
New data are added continually. The NFHL also contains map changes to FIRM data made by 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 LOMA and
LOMR-Fs. The LOMA are positioned less accurately than are the NFHL data.
Layers in the public NFHL GIS services:
Use the numbers shown below when referencing layers by number.
6. Toplogical Low Confidence Areas
8. Datum Conversion Points
16. Base Flood Elevations
19. Limit of Moderate Wave Action
21. Coastal Barrier Resources System Area
22. Political Jurisdictions
25. Primary Frontal Dunes
27. Flood Hazard Boundaries
29. Submittal Information
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
Environmental Systems Research Institute (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:
NFHL (effective data only):
Preliminary Chances Since Last FIRM (CSLF) GIS Service::
Draft CSLF GIS Service::
Preliminary National Flood Hazard Layer:
Draft National Flood Hazard Layer::
To access the service through a client like ArcGIS Desktop, you can use the service directory URL:
Then navigate to the desired service.
OGC Web Mapping Service (WMS)
Use the following URL in your GIS Application:
The WMS Capabilities file is available here:
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:
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
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.
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 Risk MAP IT Help (FEMA-RiskMAP-ITHelp@fema.dhs.gov ) or the FEMA Mapping and Insurance eXchange (FMIX) at 1-877-FEMA-MAP