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nearest one-half foot, multiplied by la, and shown as a three- digit code. For example, if the difference between water-surface elevations of the 10- and lOa-year floods is 0.7 foot, the FHF is 005; if the difference is 1.4 feet, the FHF is 015; if the difference is 5.0 feet, the FHF is 050. When the difference between the la-and lOa-year flood water-surface elevations is greater than 10.0 feet, it is rounded to the nearest whole foot. 5.3 Flood Insurance Zones Flood insurance zones and zone numbers are assigned based on the type of flood hazard and the FHF, respectively. A unique zone number is associated with each possible FHF, and varies from 1 for a FHF of 005 to a maximum of 30 for a FHF of 200 or greater. Zone A: Special Flood Hazard Areas inundated by the lOa-year flood, determined by approxi- mate methods; no base flood elevations shown or FHFs determined. Zone AS: Special Flood Hazard Areas inundated by types of lOa-year shallow flooding where depths are between 1.0 and 3.0 feet; base flood elevations are shown, but no FHFs are determined. Zones AI, A3, A4, A6, A7, and All: Special Flood Hazard Areas inundated by the lOa-year flood; with base flood elevations shown, and zones subdivided according to FHFs. Zone B: Areas between the Special Flood Hazard Areas and the limits of the 500-year flood; areas that are protected from the 100- or 500-year floods by dike, levee, or other local water-control structure; areas subject to certain types of lOa-year shallow flooding where depths are less than 1.0 foot; and areas subject to lOa-year flooding from sources with drainage areas less than 1 square mile. Zone B is not subdivided. Zone C: Areas of minimal flood hazard; not subdivided. 28