Mapping density and proportion
Sometimes
mapping an attribute with graduated colors or symbols can be misleading. A
typical case is when polygon features vary greatly in area. You may perceive patterns
in a graduated color map and assume they represent variation in the attribute
you are mapping, when in fact they reflect the variation in the area of the
features.
You can
avoid such misperceptions by mapping density—the quantity per unit of area.
Another
situation is when mapping the proportion of one quantity to another is more
important than mapping them individually. In the goat farm example, the
proportion of female to male goats in each pasture might be more important than
the total number of goats.
This topic presents methods for symbolizing maps to show density and proportion between two attributes.