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.