Consensus Report

Elevation Data for Floodplain Mapping* (2007)


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Floodplain maps serve as the basis for determining whether homes or buildings require flood insurance under the National Flood Insurance Program run by the Federal Emergency Management Agency (FEMA). Approximately $650 billion in insured assets are now covered under the program. Under a funded mandate from Congress, FEMA is modernizing floodplain maps to better serve the program. However, concerns have been raised to Congress as to the adequacy of the "base map" information available to support floodplain map modernization. The National Research Council initiated this study to advise Congress and the nation on this issue. The report concludes that there is sufficient two-dimensional "base map imagery" available from digital orthophotos (aerial and satellite photographs similar to those viewed on Google Earth) to meet FEMA's flood map modernization goals. However, the three-dimensional "base elevation data" that are needed to determine whether a building should have flood insurance are not adequate. FEMA needs land surface elevation data that are about ten times more accurate than data currently available for most of the nation. The report recommends that new, high-accuracy digital elevation data be collected nationwide using laser measurements from aircraft (lidar technology). The new data should be input into the National Elevation Dataset that the U.S. Geological Survey maintains for use in support of flood map modernization and other applications.

Key Messages

  • The nation's information for land surface elevation is inadequate to support FEMA's Map Modernization and that new national digital elevation data collection is required.
  • The committee proposes that this program be called Elevation for the Nation to parallel the existing Imagery for the Nation concept.