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

that any map product, hardcopy or digital, is rapidly outdated by new road
construction, development and other changes to the surface of the e.art:h. Thus,
in use of these data with OFIRMs, users should assess the accuracy of base map
sources to be used with OFIRMs with respect to the requi['em,~nts of the
application.

Increasingly, highly detailed large scale digital mapping is becoming clvailable.
Such data may be available from State and/or local gov~rnments, or from private
sector firms. DFIRMs may also be used in combination with these data. U::::ers
should keep in mind that even though the DFIRM map may be enlarged t.o overlay
these data, the accuracy of DFIRMs is not improved by such enlargement. As
digital maps are enlarged users may note that, the appearance of curvilinear
features of DFIRMs becoming angular, inconsistencies with large scall~ topographic
data exist, and similar issues.

Regardless of the base map source and scale of digital data used in conjunction
with DFIRMs, users should bear in mind that the DFIRM is foremost t:he result: of
hydrologic and hydraulic engineering processes, not a cartographic procHss.
Inherent in these engineering processes are many uncertainties of both data and
methodology. The resulting regulatory Base Flood Elevations (BFEs) and the
Special Flood Hazard Area (SFHA) delineations are also impacted by tolerances and
specifications used in the development of hardcopy FIRM maps. Recoqnizing these
issues, FEMA has consistently noted that the FIRM should be used as guide to the
spatial extent of flood hazards within a community. Sound judgement must: be
used, particularly when analyses performed involve areas located wi1:hin tens..of-
feet of SFHA boundary areas. FEMA guidance has been that in such cirl:umstances
comparison of the t,opographic data relative to the site or structure, and to the
BFE as determined from the flood profile in the Frs study text, is the best ml~ans
to resolve issues ("elated to floodplain location for floodplain manaqement and
insurance purposes.'

The conversion of FIRMs to a digital format is expected to have many benefits.
However, users must. bear in mind that the simple conversion of FIRMs tc, a digi.tal
format does not inherently improve the engineering quality of the product. J~any
of the same diffi.culties with interpretation of flood risk data, and the
requirement for users to apply sound judgement in methods selected for decision
making and map interpretation remains unchanged.

The "Good Faith St,andard"

The mandatory flood insurance purchase requirements of the 1973 Act apply ~nly
when a structure is located in a SFHA in a community that is participating in the
NFlP. Such a stn.:.cture must be insurable under the rules of the~ NFIP. Even
though a portion of the land parcel upon which the structure is planned may be
within a SFHA, the mandatory purchase requirement is only triggered if the
structure itself is within a SFHA.

The compliance of lenders with the mandatory flood insurance purchase require-
ments of the 1973 Act is based on a the "good faith standard." Determining
whether a structuc3 is located in an area of special flood hazard requires the
examination of the location of the structure in relationship to thl~ areas of
special flood hazard as shown on the applicable FIRM. The good fa.ith standard

10/93

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