FLOOD09505

• County: Statewide
• Basin: Statewide
• Title: Standards for Digital Flood Insurance Rate Maps
• Date: 10/1/1993
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

technical data concerning flood risk becomes available, and as some FISs be:::ome
outdated by the construction of flood control projects or the urbanizatio:~ of
rural watersheds. It is expected that with completion of all ini~:ial flood
hazard identification studies, there will be a need on a continuinq basi.3 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 NFIP mapping and engineering. After a series of technology
assessment and pilot projects, FEMA concluded that existing technology made
conversion of NFIP mapping and engineering to an automated basis feasible. In
Fiscal Year 1992, a plan was implemented to begin automation, startir.,g with the
conversion of FIRMs to a digital format.

The conversion of FIRMs to a digital format is expected to improvt~ the turn
around time for preparat ion of new and revised FIRMs and decrease some costs
related to preparing FIRMs. In the future, digital FIRMs (DFIHMs I may also
provide the data base for automation of the massive FIRM storage, retrieval, and
distribution system. In addition to these internal benefits, FEMA also ex~ects
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 rr,aintenance
tasks. To encourage use of the DFIRMs, FEMA established a credi'ting plan for
local government use of GIS technology and DFIRMs as an element of thE' Community
Rating System ("National Flood Insurance Program Conununity Rating System
Coordinator's Manual", FIA Publication No. 15, October 1990).

A key consideration in design of the digitizing process was to ident:ify and a,dopt
a standard format for digital FIRM data. It would be impossiblE! for FEMA to
assure that all end-users would have the same mapping software, or for FE~A to
support all mapping software data formats. Therefore, FEMA has ele~ctHd to a.dopt
a single standard for DFIRMs. Prime considerations in the selection .of a
standard were:

o compatibility with vector data structures;'
o support of topological data structure;
o data import and export compatibility with most public and prc'pri-
etary GIS and automated mapping software packages;
o forward compatibility with future developments in the are,l of
digital map standards, particularly the Spatial Data Transfer
Specificat~on;
o documentation; and
o support and maintenance by a major public agency.

After evaluating digital map data formats meeting these criteria, n:MA determined
that the U.S. Geological Survey (USGS) Digital Line Graph LevE,l 3 (DLG-3),
Optional Format, best met these criteria and the needs of the NFIP. Subsequent-
ly, FEMA coordinated with the Nation Mapping Oivision of the USGS te. establish
a topological structure for digital FIRMs consistent with USGS OLG-3 specifica-
tions and to assigI1 major and minor attribute codes to features that did not

10/93

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