1982-1985 Map Initiatives Project (MIP) Determined Flood Map Format

The first maps produced under the NFIP were community-based and consisted of two similar,
but different formats. One, the Flood Insurance Rate Map (FIRM) was produced for use by the
insurance industry for the purpose of determining flood insurance rates. The other, the Flood
Boundary and Floodway Map (FBFM) was intended to be used by state and local floodplain
administrators for floodplain management purposes. Both used the same base map as the
underlying layer for landmarks, such as major streets and highways, railways, and rivers, and
both were truncated at the municipal border. But that is the limit of the similarity between the
two formats.

FIRMs defined the limits of the floodplain of both the 1% chance flood and the 0.2% chance
flood (500 year) and included the BFE and flood ‘zones’ to aid the insurance agents determine
the correct flood insurance premium. Similarly, the FBFM included the same delineation of the
1% and 0.2% flood but did not include the BFE. Instead, the FBFM showed the locations of
critical cross-sections and the floodway boundaries, where defined. Ironically, the floodway was
unshaded, no different than the land area outside the 0.2% chance flood. It could be, and was,
misinterpreted as land outside the SFHA though.

Mapping was focused on urbanized areas first and rural lands later. It was not uncommon for a
city to be mapped only to have the less developed county surrounding the city mapped several
years later. This resulted in lands that were annexed by the city between the time the two maps
were produced to be omitted on both maps — outside the city when its map was produced and
no longer part of the surrounding county when its maps were produced — leaving gaps in the
maps of the SFHA and flooding sources.

In 1983, FEMA hosted a review of multiple mapping formats by a Task Force composed of
ASFPM — represented by the Mapping & Engineering Standards Committee and the Flood
Insurance Committee — and the Federal Insurance Administration (FIA) and State and Local
Programs & Support (SLPS) of FEMA. That review led to the creation of the Mapping Initiatives Project Steering Committee (MIPSC) in 1984 and the development of a questionnaire that was ultimately filled out by nearly 600 constituents. Approximately half of the responses were provided by state and local floodplain managers, engineers, land surveyors, and realtors and the other half by representatives of the insurance and banking industry.

The result
Based on the survey results the mapping format was changed starting in mid-1985 to the single-
map format still used today. The MIP also set in motion the decision to undertake Flood
Insurance Studies (FIS) on a county-wide basis to eliminate the creation of gaps in the SFHA due
to annexations.

Interestingly, the insurance and banking industry representatives strongly favored mapping the
limits of the SFHA based on visibly identifiable features, such as roads, highways, and railways
rather than topography because it made decisions regarding ‘in’ or ‘out’ easier. However, that
approach required first defining the SFHA based on topography, then calculating what
percentage of an area, such as a city block, was below the BFE. If more than 50% of the block
was below the BFE, the map would be revised to reflect the entire block within the SFHA. If less
than 50% of the block was below the BFE, then the map would be revised showing the entire
block outside the SFHA.

Ultimately this format, known as “rectilinear” flood hazard delineation, was not selected due in
part to the added costs as well as the concern that too many people would choose to avoid
purchasing flood insurance regardless of whether their property was below the BFE.
The final report on the Mapping Initiatives Project (MIP) was published in January 1985 and a
hard copy is available from ASPFM’s library.