Fig. 2

Denominator estimation for a hypothetical part of study zone A. The population for those aged 15 through 19 for each tract (P _t ) is multiplied by the proportion of the tract, or areal weight (A _zt /A _t ), in the study zone. The output for each tract (E _pt ) in the entire zone is summed to obtain a population estimate for the study zone. Note: For graphic simplicity, only a subset of zones are shown in the figures. Methods are the same for each of the four study zones, A, B, C, and D