The upper left plot (a) shows the distribution of the 1980 Census population of non-Hispanic white females of ages 45-64. Each dot, plotted at random within its census tract, represents a population of 20 women. The population is mostly concentrated in a few urban areas.
The upper right plot (b) shows the distribution of 68 cases, each plotted at random in its census tract of residence. Three cases with unknown census tract of residence were omitted. As expected, the distribution of cases in (b) reflects the population distribution in (a).
In the lower left plot (c) the tract boundaries have been adjusted by a DEMP transformation. Each dot, plotted at random within the transformed boundaries of its census tract, represents 20 women. Figure (c) shows that population density has been almost perfectly equalized by the DEMP transformation.
In the lower right plot (d) each of the 68 cases is plotted at random within the transformed boundaries of its census tract. There is a hint of nonuniformity, corresponding to a reduction of (age-race-ethnicity-specific) risk in Berkeley relative to adjacent areas in Richmond and Oakland. Statistical techniques are required to determine the significance of the apparent non-uniformity in (d).
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1978-82 breast cancer cases, distant, non Hisp white females 45-64
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cases in Alameda and Contra Costa counties
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Density Equalizing Map Projections