There are three basic types of flood hazard zones shown on a flood insurance map.
Zones that start with an "A" (A, AE, AH, AO) are 100-year floodplains that are determined by a Flood Insurance Study. In most instances, base flood elevations (the elevation of the predicted flood level) are derived from detailed hydraulic modeling.
Zone X shows area outside the 100-year floodplain, but within the 500-year floodplain.
Finally, floodways are located in the immediate vicinity of the stream and depict areas of high flood hazard.