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 by replacing maps that contain inaccurate spatial definitions and that lack base flood elevations with maps that accurately define the spatial extent of the SFHA and provide base flood elevations. The marginal benefits derived from these more accurate maps exceed the marginal costs of their preparation. Determination of base flood elevations produces the greatest increment of benefits.

Finding. No single approach to map preparation is appropriate for all circumstances. The benefits and costs of each method are risk and vulnerability dependent.

Recommendation. The flood study method should be determined based on the accuracy of the topographic data in the county or watershed under study and the current and future risk to those in the mapped area.