FEMA

NFHL Web Map
Service (WMS)
Add Flood Hazard Map Layers to Your Geographic
Information System (GIS) Application
Purpose and Appropriate Use
The Federal Emergency Management Agency (FEMA) provides access to the
National Flood Hazard Layer (NFHL)1 and related data through a Web Map
Service (WMS). You can use the service to add web-based digital flood
hazard maps to business applications. You also can look up attribute
information for data portrayed on the maps. FEMA publishes new Flood
Insurance Rate Maps (FIRMs) in the form of paper maps, digital map images
and digital geospatial flood hazard data like those in the NFHL. When used
appropriately, these representations are equivalent to one another and
represent official FEMA designations of Special Flood Hazard Areas (SFHAs),
base flood elevations (BFEs), insurance risk zones and other regulatory
information.
If you plan to use the map images provided by the WMS for official
purposes, ensure that imagery and other map information displayed with
the flood data meet FEMA’s standards for map accuracy2.
What is a WMS?
A WMS is a web-based service that generates map images from a database
containing spatial information and delivers these images over the Internet. A
WMS also can retrieve attribute information for the data portrayed in the
image. The image files generated by a WMS contain information about the
location on the earth’s surface portrayed by the image. To create custom
maps, a computer mapping program uses this location information to
register WMS map images to other map information. For example, you can
use GIS software to overlay map images from a WMS on your map data.
Computer programs request the images or attribute information using URLs
defined by the WMS specification. The FEMA service complies with version
1.1.1 of the WMS specification. The specification, developed by the Open
Geospatial Consortium, Inc. ®, is available at
http://www.opengeospatial.org/standards/wms. To use a WMS, you need
web-based mapping or GIS software, or software that you develop that
displays WMS images and a high-speed Internet connection.

Viewing Flood Hazard Data in Your GIS Using
the NFHL WMS
FEMA’s WMS named NFHL portrays the full range of
NFHL map features. Areas of high flood hazard are
symbolized in red (see Figure 1). The symbols were
designed to be legible when overlaid on imagery.

Figure 1. Portion of a map image returned by the NFHL WMS. Only a few of
the available map layers are shown. The image is for an area in Pittsburgh,
Pennsylvania.
Computer mapping programs have different means for
accessing a WMS. Some only require you to enter a URL
while others require you to provide additional software.
See the documentation for your software to learn how to
add a WMS.
Regardless of how your software works, you will need
one or more of the following URLs to access the NFHL
WMS. The service responds to the GetCapabilities,
GetMap and GetFeatureInfo requests defined by the WMS
specification. Many software applications only need the
GetCapabilties URL to access a WMS.
The NFHL service:
?? Responds to GetCapabilities requests through the URL:
https://hazards.fema.gov/wmsconnector/wmsconnector
/Servlet/NFHL?REQUEST=GetCapabilities&SERVICE=W
MS
?? Responds to GetMap requests through the URL:
https://hazards.fema.gov/wmsconnector/wmsconnector
/Servlet/NFHL?VERSION=1.1.1&REQUEST=GetMap&
(the WMS GetMapparameters that describe a particular
map)
?? Responds to GetFeatureInfo requests3 through the URL:
https://hazards.fema.gov/wmsconnector/wmsconnector
/Servlet/NFHL?VERSION=1.1.1&REQUEST=GetFeatureIn
fo& (the WMSGetFeatureInfo parameters that describe a
particular map, and the layer(s) and the location on the
map for which attribute information is requested)

NFHL Data Are Organized as Map Layers
The NFHL WMS makes information available as map
layers. Each layer displays a theme of data, such as flood
hazard areas, floodways, cross sections and coastal
transects. Each layer has a name, a title, a set of map
symbols and a range of map scales for which the service
provides a map image. View the list of layer titles and
associated map symbols at
https://hazards.fema.gov/femaportal/resources/symbolo
gy.htm.
The service also provides reference information that
complements the DFIRM data in the NFHL. For areas for
which flood hazard data are not available from the NFHL,
a map layer portraying an older set of flood hazard data,
named the “Q3” data, might be available. Another layer
displays the approximate locations of places described in
Letters of Map Amendment (LOMAs) and Letters of Map
Revision Based on Fill (LOMR-Fs) and their case
numbers. The service also provides map layers that
display flood data and flood map availability and a
version of the national FIRM panel scheme.
Accessing Commonly-Used Layers
Five information themes are of common interest to users:
flood hazard zones, cross sections, communities, FIRMs
and LOMRs (see Figure 2). These themes are available
using the layers listed below.
Figure 2. Map image of commonly used layers from the NFHL WMS overlaid in 3D on imagery and terrain data in Google Earth™4. The area is the
same shown in Figure 1.

3 The GetFeatureInfo function returns table, attribute and value information for layers identified in the
URL. Find specifications for the tables, attributes and values in the DFIRM database specifications. See
section L7, “Database Table Structure for Preliminary and Final Digital Flood Insurance Rate Map
Databases,” in Appendix L, “Guidance for Preparing Draft Digital Data and DFIRM Databases,” of
Guidelines and Specifications for Flood Hazard Mapping Partners. Appendix L is available through
http://www.fema.gov/library/viewRecord.do?id=2206. A WMS layer has one corresponding DFIRM
database table.
4 Names of products are provided for descriptive purposes only and do not represent an endorsement by
the United States Government.

?? Flood hazard zones: The layers titled “Flood Hazard
Zones (Detailed)” and “Flood Hazards Zone Boundaries”
show insurance risk zones with red (high hazard), pink
(medium-to-low hazard) and gray (undetermined
hazard) line patterns and outlines. Areas of low hazard
are not shaded.
?? Cross sections: When used with the Flood Insurance
Study for the community, cross sections are the basis for
calculating a BFE. The layer titled “Cross Sections” shows
cross section lines and labels in orange.
?? Communities: The layers titled “Jurisdiction Names” and
“Jurisdiction Boundaries” show the names and
boundaries with brown text and line symbols. If you use
both layers and see a name but no boundary, the entire
WMS image is within the community.
?? FIRMs: The layer titled “DFIRM Panels (detailed)” shows
the 11-character number and boundaries of FIRM panels
in light blue. If you see a number but no boundary, the
entire WMS image is within the panel.
?? LOMRs: The layer titled “LOMR’s” shows the case
number and boundaries of effective LOMRs in dark blue.
If you see a number but no boundary, the entire WMS
image is within the LOMR. All of these layers display
information at map scales of 1:32,000 and larger. Some
also display information at smaller map scales.
NFHL WMS Tips and Tricks
My application has an option of identifying a background
color (a color that my application makes transparent).
Which color should I choose?
“White,” red-green-blue (RGB) code 255,255,255.
Instead of an image, the WMS returns the message
“Requested image is too big and cannot be created.”
What should I do?
The maximum image size is 1024-by-1024 pixels.
Change the WIDTH and HEIGHT parameters in your
GetMap URL to request an image of
1024-by-1024 pixels or smaller.
If you cannot control these parameters directly:
?? Make your map window smaller until an image appears.
?? If you need a large map window, see if your application
will tile the WMS images. In this approach, the
application requests multiple smaller images from the
WMS and tiles them to fill a large area. One drawback of
this approach is that labels for features that span tiles will
be repeated for each tile. For example, the name of a
community that spans three tiles will be repeated on each
tile.
The whole image is covered by purple solid or vertical
striped shading. How do I turn this off?
Turn off the layer “DFIRM Data Availability” (for solid
shading) and “Flood Map Availability” (for striped
shading).
I would like to see through the image when I overlay it
on other maps. What are my options?
Options include:
?? Use the image “as is.” Most area shading uses a weave
pattern that you can see through if the color “white” is
set to be transparent.
?? If your application permits it, make the image
transparent. If you would like some layers to be
transparent and not others, add the WMS to your
application twice. In one instance of the WMS, only turn
on the layers to be transparent and set the transparency
parameter. In the other instance, only turn on the layers
to be solid.
Why are there two “Q3 Flood Hazards” layers?
“Q3 Flood Hazards (red)” is easier to see over imagery,
has the color of similar DFIRM flood hazard data, and is
recommended. “Q3 Flood Hazards” was retained for
backwards compatibility with existing applications. They
show the same information.
Why are there three layers for “Flood Hazard Zones
(General)”? Should they be used together?
The three layers allow for flexibility in map display. The
layer shows all “A” (A, AE, AH, etc.) and “V” (V and VE)
zones in one symbol; the “Shaded X” zone in another
symbol; and the “D” zone in a third symbol. If you want
to show this generalized information throughout the
scale range, use “Flood Hazard Zones (General).” If you
want to show generalized zone information at medium
map scales, but detailed zone information (i.e.,
distinguish between zones A, AE, AO, V, VE, etc.) at large
map scales, use “Flood Hazard Zones (General-med)” and
“Flood Hazard Zones (Detailed)” together. Do not use all
three layers together.

When should I use the Mask Layers?
www.fema.gov/plan/prevent/fhm/rm_main.shtm · 1–877–FEMA MAP
Use the Mask Layers with one or more of the “Flood Hazard Zones” layers (general or detailed) to distinguish where there
are no flood hazard data in the NFHL. When sequenced in the drawing order (from top to bottom) “Flood Hazard Zones”
(general or detailed), “Flood hazard zone (mask)” and “No DFIRM mask,” the display shows zones A, V, Shaded X, and D
in red, pink and gray; Zone X and open water in white, and areas for which there are no data (including flood hazard areas
coded as “area not included”) in yellow. If an area has overlapping polygons coded as “area not included” and as one of the
zone designations, it will be shaded with the zone designation.

5 Labels for many layers display at map scales of 1:32,000 and larger only.
6 Same as Flood Hazard Zones (General) except for the scale range.
7 Same as Flood Hazard Zones (General) except for the scale range.
8 Recommended. Same as Q3 Flood Hazards except for symbology.
9 Maps available from the MSC. Due to different maintenance schedules, this layer might not match the DFIRM Panels (detailed) layer.
10 Created for a particular application. Not useful to most applications.
11 Created for a particular application. Not useful to most applications.

Sources of Additional
Information
FEMA web site for the NFHL
WMS: See the MSC web site
at http://msc.fema.gov. In
the area for NFHL-related
services, follow the link “Use
Web Map Service (WMS) in
your own GIS application.”
Questions or comments
about the NFHL WMS: Direct
them to
miphelp@riskmapcds.com.
Please include the words
“NFHL WMS” in the subject of
your message. Note that
FEMA may not be able to
answer questions about how
to use the WMS with a
specific software application.
To view and buy flood maps
and data: See the MSC Web
site at http://msc.fema.gov.
1 The National Flood Hazard Layer is a computer database
that contains the digital flood hazard information from
FEMA’s Flood Map Modernization program. These map
data include Digital Flood Insurance Rate Map databases
and later changes made by Letters of Map Revision. They
do not include changes identified by property description.
Maps that have not been modernized are not available in
the NFHL, but can be viewed and ordered from FEMA’s
Map Service Center at http://msc.fema.gov.
2 A base map shows the location of roads and railroads,
streams and lakes, boundaries, structures, and other
features. When used with flood hazard data for official
purposes, base maps must have a horizontal radial
accuracy (Accuracyr) better than or equal to 38 feet
(11.58 meters) as measured using the National Standard
for Spatial Data Accuracy. (This measure is equal to maps
of scales larger than or equal to 1:12,000 under the old
National Map Accuracy Standard.)

www.fema.gov/plan/prevent/fhm/rm_main.shtm

1-877-FEMA MAP

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