FLOOD02115

• County: Statewide
• Basin: Statewide
• Title: National Flood Insurance Program Standards for Digital Flood Insurance Rate Maps
• Date: 10/1/1993
• Prepared By: FEMA
• Floodplain - Doc Type: Educational/Technical/Reference Information

technical data concerning flood risk becomes available, and as some FISs become
outdated by the construction of flood control projec~ts or the urbanization of
rural watersheds. It is expected that with comple1:.ion of all initial flood
hazard identification studies, there will be a need on a continuing basis to'
update several thousand FIRMs per year.

Automation of NFIP Mapping and Engineering

Developments in the fields of automated cartography and Geographic Information
Systems (GIS) technology during the 1980's led to FEMA's study of the feasibility
for automating NFlP mapping and engineering. Afte'r a series of technology
assessment and pilot projects, FEMA concluded that existing technology made
conversion of NFlP mapping and engineering to an autc:nnated basis feasible. In
Fiscal Year 1992, a plan was implemented to begin automation, starting with the
conversion of FIRMs to a digital format.

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The conversion of FIRMs tC' a digital format is exp!cted t.... improve the turn
around time for preparat,ic.., of new and revised FIRMs and .' -lcrease some costs
related to preparing FIRMs. In the future, digital FIRMs (DFIRMs) may also
provide the data bas~ for automation of the massive FIRM storage, retrieval, and
distribution system. In addition to these internal b,enefits, FEMA also expects
FIRM end users, particularly those at the State and local government level, to
benefit from the increased capability to perform analytical and administrative
tasks required under the NFIP and to automate FIRM revision and maintenance
tasks. To encourage use of the DFIRMs, FEMA establi.shed a crediting plan for
local government use of GIS technology and DFIRMs as a,n element of the Conununity
Rating System ("National Flood Insurance Program Conununity Rating System
Coordinator's Manual", FIA Publication No. 15, OctobE~r 1990).

A key consideration in design of the digitizing proces" was to identify and adopt
a standard format for digital FIRM data. It would be impossible for FEMA to
assure that all end-users would have the same mappin9 software, or for FEMA to
support all mapping software data formats. Therefore, FEMA has elected to adopt
a single standard for DFIRMs. Prime considerations in the selection of a
standard were:

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compatibility with vector data structurefi;'
support of topological data structure;
data import and export compatibility with most public and
etary GIS and automated mapping software packages;
forward compatibility with future developments in
digital map standards, particularly the Spatial
SpecificatJ.oni
documentation; and
support and maintenance by a major public agency.

propri-

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the
Data

area of
Transfer

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After evaluating digital map data formats meeting these, criteria, FEMA determined
that the U.S. Geological Survey (USGS) Digital Line Graph Level 3 (DLG-3),
Optional Format, best met these criteria and the needs of the NFIP. Subsequent-
ly, FEMA coordinated with the Nation Mapping Division of the USGS to establish
a topological structure for digital FIRMs consistent ..ith USGS DLG-3 specifica-
tions and to assigrt major and minor attribute codes to features that did not

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