Dot Density Mapping and Symbol Gradients: Dot density maps can be a good
alternative to choropleth maps because you can show the raw variable without
normalizing it but the map viewer still gets an idea of how it is distributed. For
example, a population map can show a dot for every 10,000 people in each
county, with the dot(s) being placed somewhere inside the county polygons.
In this way the map viewer need only look at the differences in the numbers
of dots in each county to compare them as opposed to using a legend to help
interpret a color gradient. Of course, a legend would still be needed to provide
the ratio of dots to people, but it would still wind up being less work for the
map viewer to glance at that ratio once as opposed to going back and forth
between colors on the map and the legend. See the soils section of Chapter 6,
“Features,” for another application of dot density mapping.