Using Digital Flood Hazard Data in the National Flood Insurance Program. FGDC Coordination Working Group Scott McAfee Paul Rooney. April 5 th , 2005. FEMA is responsible for identifying areas of special flood hazard. FEMA publishes Flood Insurance Rate Maps or Flood Hazard Boundary Maps.
FGDC Coordination Working Group
April 5th, 2005
FEMA publishes Flood Insurance Rate Maps or Flood Hazard Boundary Maps.
Traditionally published as paper documents.
Paper version was considered the official legal version for the purposes of the NFIP.National Flood Insurance Program (NFIP)
Congress included a section establishing digital geospatial flood hazard data distributed by FEMA as having equivalent legal standing to the paper maps.
"For the purposes of flood insurance and floodplain management activities conducted pursuant to the National Flood Insurance Program under the National Flood Insurance Act of 1968 (42 U.S.C. 4001 et seq.), geospatial digital flood hazard data distributed by the Federal Emergency Management Agency, or its designee, or the printed products derived from that data, are interchangeable and legally equivalent for the determination of the location of 1 in 100 year and 1 in 500 year flood planes, provided that all other geospatial data shown on the printed product meets or exceeds any accuracy standard promulgated by the Federal Emergency Management Agency.“NFIP Reform Act of 2004
Flood maps are the central tool for risk identification, floodplain management and insurance in the NFIP.
Numerous stakeholders are required to use.
Interpretation can have substantial impacts on specific properties and landowners.Flood Maps Are Key to Regulation
Stakeholders are still able to use the paper maps. floodplain management and insurance in the NFIP.
Legal status does not result in costly or damaging disagreements between digital geospatial maps and paper maps.
Encourage the use advanced technology and quality local data to make administration of the NFIP more efficient and effective.Goals
FEMA has been implementing digital geospatial versions of the flood maps over the last several years.
Existing policy already makes it possible for communities to use these digital geospatial products in the administration of the NFIP.
Insurers, lenders and flood determination companies must rely on the paper maps as the official designation flood hazards.Current Status
Significant advantages in capability, precision, and cost for users who are able to use digital geospatial data products.
Stakeholders who have already adopted digital technology will be able to use it for NFIP purposes.
Cost savings can be achieved by reducing the number of paper maps that have to be printed and distributed.Benefits of Digital Data
Traditionally, FEMA for users who are able to use digital geospatial data products.’s maps have provided only roads, railroads, streams and community boundaries as reference features for interpreting the maps.
Base map features have been considered integral to the definition of the flood hazard.
This practice is technically wrong from a mapping standpoint
Users cannot benefit from the capabilities of digital geospatial data and advances in mapping technology with this interpretation.Status of Base Map
Surveying and mapping in the United States is based on a geodetic control network National Geodetic Survey (NGS).
FEMA’s new maps include a coordinate grid system as a reference
Define the location of the flood hazard by defining it relative to the NSRS rather than roads.National Spatial Reference System (NSRS)
Clarify policy to identify the coordinate grid as the controlling definition of the areas of special flood hazard rather than the roads or other base map features shown on the mapProposed Policy
Eliminate any difference between the paper and the digital geospatial maps.
Locations accurately measured relative to a standard coordinate system will be precisely the same on this paper map as in the digital geospatial version of the map.
Enable communities to substitute their own, more accurate base maps for the default base map provided by FEMA.
New streets can be added or improved local mapping can be used without waiting for FEMA to revised official map.
Coordinate grid as authoritative is less intuitive and more complicated for some maps users to understand.Advantages / Disadvantages
Appears to be consistent with the intent of the Act. geospatial maps.
The reform act says, “provided that all other geospatial data shown on the printed product meets or exceeds any accuracy standard promulgated by the Federal Emergency Management Agency.”
Indicates the user may use data that meet FEMA standards, but were not used by FEMA on the original published flood map.Intent of the Reform Act
The FHBM or FIRM may be published as paper maps, digital map images or digital geospatial flood hazard data. Where FEMA publishes the official FHBM or FIRM in a digital form, the digital versions, published paper version and printed versions produced from the digital file are considered the official FEMA designation of the areas of special flood hazard, base flood elevations, insurance risk zones and other regulatory information. For official FHBM or FIRM maps that are available as digital geospatial data (the DFIRM Database product) the horizontal location of the flood hazard information is defined with respect to the primary coordinate grid system shown on the map and the coordinate reference system of the digital geospatial data, not with respect to the base maps features. Where there are conflicting interpretations regarding the precise horizontal location of the areas of special flood hazard, the coordinates of the flood data will be considered authoritative. Printed products derived from the digital geospatial data are legally equivalent to the official FHBM or FIRM provided the base map meets the FEMA base map accuracy standard and the map includes coordinate reference information consistent with FEMA’s mapping specifications.Recommended language for the policy guidance:
For the purposes of this definition, the base map is the set of physical and cultural features shown on a flood map to provide a reference context to the flood hazard information. Base map features include roads, railroads, buildings, lakes, streams, shorelines, community boundaries, public land survey system information, land parcel, and orthoimagery.Base Map
Paul Rooney of physical and cultural features shown on a flood map to provide a reference context to the flood hazard information. Base map features include roads, railroads, buildings, lakes, streams, shorelines, community boundaries, public land survey system information, land parcel, and orthoimagery.
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