ArcNews Online

Summer 2008
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In 1968, Congress passed the National Flood Insurance Act and created the National Flood Insurance Program (NFIP). The act mandated that the nation's flood zones be established in order to define locations subject to higher probability of flooding. Paper maps were created to show the location of 100-year floodplains. Properties in a 100-year floodplain have a 1-in-100 chance to flood in any given year and are thus labeled Special Flood Hazard Areas (SFHAs).

Specific building standards and flood insurance rates were assigned to SFHAs, and risk zones were established and designated by a letter or series of letters. AE Zone, for example, denotes a floodplain with a 100-year elevation, while VE Zone identifies flooding along a coastline. Shaded X Zone areas have a low to moderate risk of flooding and are located in a 500-year floodplain, while X Zone areas are outside a 500-year floodplain.

The result of detailed topographic and hydraulic studies was state-of-the-art paper flood insurance rate maps (FIRMs), first printed in 1973. FIRMs became the official source of data for determining if a structure was located in a flood zone and were used to establish flood insurance rates and building codes.

As digital technology evolved, computer-aided design (CAD) files were used in the 1980s to process and produce paper FIRMs. In the 1990s, Windows-supported applications were common on desktop computers, and the Federal Emergency Management Agency (FEMA) answered with digital FIRMs in an early GIS format called Q3. Because the floodplain data provided was compressed into a single layer of zones, Q3 maps were void of some paper map features, such as base flood elevations, river cross sections, study data, and river depths.

Paper maps and Q3 data were preempted in 2004 when FEMA, Congress, and president George W. Bush recognized the value of digital flood insurance rate maps (DFIRMs) and initiated the Map Modernization program. As part of its mission to reduce loss of life and property from all types of hazards, FEMA's Mitigation Division oversees the production of DFIRMs, all of which are being released in GIS formats.

See also "GIS-Based Flood Mapping at FEMA."

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