Figure 6.103 This soils map uses a dot density technique. Each soil map unit is comprised of several types of soils (shown here are the four main soil orders in this particular taxonomy) that are shown as randomly placed dots in the units depending on the percentage of the unit that each comprises. So if a soil unit is made up of 70 percent Spodosols and 30 percent Entisols, then it will have seven Spodosol dots (brown in this case) and three Entisol dots (blue in this case). These data are from the NRCS STATSGO database map unit polygons and joined with the “comp” table from the same data source. The size of the mapping unit affects the visual outcome of a dot density map as you can see in this example. Both large and small soil units contain ten dots, so the larger units have more blank space. Of course, the dots in the smaller units are squeezed together. You can change the symbol sizes and the number of percentage points each dot represents until an optimal compromise is made.