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Mapping the Zone: Improving Flood Map Accuracy
of quantifying some kinds of benefits. Nevertheless, because all of the costs but only some of the benefits were considered, the results are likely the right order of magnitude, suggesting that more accurate maps produce net benefits for the nation.
Finding. Significant flood losses could be avoided byreplacing maps that contain inaccurate spatial definitions and that lack base flood elevations with mapsthat accurately define the spatial extent of the SFHAand provide base flood elevations. The marginal benefits derived from these more accurate maps exceedthe marginal costs of their preparation. Determination of base flood elevations produces the greatestincrement of benefits.
Finding. No single approach to map preparationis appropriate for all circumstances. The benefitsand costs of each method are risk and vulnerabilitydependent.
Recommendation. The flood study method shouldbe determined based on the accuracy of the topographic data in the county or watershed understudy and the current and future risk to those in themapped area.