<P> A dot distribution map might be used to locate each occurrence of a phenomenon, as in the map made by Dr. Snow during the 1854 Broad Street cholera outbreak, where each dot represented one death due to cholera . Where appropriate, the dot distribution technique may also be used in combination the proportional symbol technique </P> <P> A dasymetric map is an alternative to a choropleth map . As with a choropleth map, data are collected by enumeration units . But instead of mapping the data so that the region appears uniform, ancillary information is used to model internal distribution of the phenomenon . For example, population density will be much lower in forested area than urbanized area, so in a common operation, land cover data (forest, water, grassland, urbanization) may be used to model the distribution of population reported by census enumeration unit such as a tract or county . </P>

Shows specific theme or data about an area