The Federal Emergency Management Agency, or FEMA, is responsible for mapping flood zone areas in the US for the National Flood Insurance Program. Flood zones, or Special Flood Hazard Areas (SFHAs) get depicted on Flood Insurance Rate Maps (FIRMs).
For much of the US, GIS flood data is available from FEMA in either DFIRM Database format or as Q3 Digital Flood Data from the FEMA Map Service Center. DFIRM databases are much more comprehensive, and contain all the elements necessary for producing a FIRM. Digital Q3 Flood Data are 1:24,000 scale data developed by scanning existing Flood Insurance Rate Maps and vectorizing a thematic overlay of flood risks.
For North Carolina, however, it is not recommended to use older Q3 data. Instead, for the most current flood zone information, use maps and data produced by the North Carolina Floodplain Mapping Program discussed below. Superceded North Carolina Q3 data are still available and also discussed below.
North Carolina Floodplain Mapping Program Data
In North Carolina, following Hurricane Floyd, the North Carolina Floodplain Mapping Program was established to work with FEMA and other cooperators to map all the of the state's flood zones. As of late 2008, the work is mostly completed (Status graphics ).
Data from this work can be downloaded from the NC Floodplain Mapping Information System . Using the "Download Data" tab along the top of the window, the following data products are available by county:
- Personal Geodatabase and shapefiles of flood zone areas and many other county GIS data layers that were used to model and create flood zone maps. There is also a Geodatabase Dictionary in PDF, which documents the Personal Geodatabase.
- Digital Flood Insurance Rate Maps (DFIRMs) - flood zone maps produced by FEMA in PDF. Use index maps available here, the DFIRM Panel Shapefile, or Geodatabase layer to find the panel(s) you need.
- Flood Insurance Study (FIS) Report, in PDF
- LiDAR Data: Bare Earth as well as 20ft and 50ft spaced DEM points. For instructions on how to import the LiDAR data, and for sources of derivative data products, see the Elevation Data webpage.
For those who prefer not to download data or use GIS, online mapping capabilities are also available on the Floodplain Mapping website.
Digital Q3 Flood Data
Digital Q3 Flood Data are GIS data which depict flood zone polygons shown on older FIRMs, and are produced via a scanning and vectorization process. Vector Q3 Flood Data files contain only certain features from the existing FIRM hardcopy and are organized into single countywide files.
The vectorized features contained in digital Q3 Flood Data files include:
- Annual chance floodplain areas of 1 and 0.2 percent
- Zone V areas, certain floodway areas, and zone designations
- Coastal Barrier Resources Act (COBRA) areas
- Political areas, including community identification numbers
- FIRM panel areas, including panel number and suffix
- 7.5-minute quadrangle areas
- Mappable Letters of Map Change (LOMCs)
What are some limitations of Q3 data?
Digital Q3 Flood Data are not tied to a base map, are not used to produce a new version of the FIRM hardcopy, and are not subjected to community review. The Q3 data does not provide base flood elevation information; thus, it has limited application for engineering analysis, particularly for site design or rating flood insurance policies for properties located within Special Flood Hazard Areas (SFHAs). Since the geographic processing performed to develop digital Q3 Flood Data may introduce differences with the FIRM hardcopy source, users must apply considerable care and judgment in the application of this product. For instance, digital Q3 Flood Data may be overlaid on highly detailed large-scale community base mapping data, but, if parcel level determinations are made, they must be prefaced with information about the accuracy of the data from which they are derived. (Source: >FEMA Digital Q3 Flood Data Web Site, no longer online)
What can the Digital Q3 Flood Data be used for?
The digital Q3 Flood Data are designed to provide guidance and a general proximity of the location of Special Flood Hazard Areas. The product is designed to support planning activities, some Community Rating System activities, insurance marketing, and mortgage portfolio reviews. The digital Q3 Flood Data product can be a valuable tool in screening property addresses within a GIS to determine flood risks. (Source: FEMA Digital Q3 Flood Data Web Site, no longer online)
Please Note: For North Carolina, Q3 data is NOT the most current or accurate flood zone dataset. Instead use data from the North Carolina Floodplain Mapping Program, discussed above. Q3 data are still available and documented here for those who may want to refer to the older delineations.
Q3 FEMA Flood Data are available for the following 53 North Carolina counties: Alamance, Beaufort, Bertie, Bladen, Brunswick, Buncombe, Cabarrus, Camden, Carteret, Columbus, Craven, Cumberland, Currituck, Dare, Davidson, Duplin, Durham, Edgecombe, Forsyth, Franklin, Granville, Greene, Guilford, Halifax, Harnett, Henderson, Hoke, Hyde, Johnston, Jones, Lenoir, Mecklenburg, Moore, Nash, New Hanover, Onlsow, Orange, Pamlico, Pasquotank, Pender, Person, Pitt, Randolph, Robeson, Rutherford, Sampson, Scotland, Vance, Wake, Warren, Watauga, Wayne, and Wilson. All available Virginia, South Carolina and Georgia data is available offline.
Specifications and Documentation
FEMA flood data are available in ARC/INFO, MapInfo and DLG format. The ARC/INFO and MapInfo versions are in geographic coordinates/decimal degrees. The DLG versions are in UTM/meters. The Datum is NAD 27. (Note: the NCDOT versions of the data are in State Plane NAD 83 feet or meters as ArcInfo or Microstation files). The scale is 1:24,000.
Q3 Data Access
Q3 data for the above counties is accessible via the Geodata Server in the /fema/q3flood/ directory, or FTP to ftp://gisdata.lib.ncsu.edu/fema/q3flood/. The data files are in ArcInfo coverage format and .e00 format. File names correspond to North Carolina county FIPS codes. As stated above, these coverage are in geographic coordinates.
NC CGIA's BasinPro 8 contains the same NC Q3 data as above, but compiled into two seperate shapefiles - one for eastern NC and one for western NC. See the Detailed Data Records for Eastern NC and Western NC for access.
State Plane NAD 83 (meters and feet) versions of this data are publicly downloadable (North Carolina data only) as ESRI shapefiles or Microstation design files from North Carolina Dept. of Transportation at: http://www.ncdot.org/it/gis/DataDistribution/FEMAFloodData/default.html
MapInfo and DLG versions are available on CD-ROM. Selected MapInfo and DLG versions will be made network accessible upon request to Data Services.
Flood Data Live Web Mapping
FEMA flood hazard data can be viewed online using: