Mapping proportion

You can map the relationship between two attributes by normalizing (dividing) one by the other to produce a ratio. As when mapping density, normalized data is typically symbolized using graduated colors or symbols.

Common reasons to map attribute relationships
What to map	Example
Proportion of the part to the whole	Countries: Bushels of wheat exported normalized by bushels of wheat harvested
Rate of something	Counties: Cases of heart disease normalized by total population
Relationship of one characteristic to another	Schools: Number of students normalized by the number of teachers
Relationship of one time period to another	Sales territories: Last year's sales revenue normalized by this year's sales revenue

Proportions can be represented in a legend in a number of ways. Three common ways are to use:

· Ratios, which range between 0 and 1

· Percentages (ratios multiplied by 100)

· Rates based on a round number, such as per capita (per person), per 100, or per 1,000

The ratio of children to adults is mapped by normalizing one attribute by another. Two alternative legends are shown: the top one uses ratios, while the bottom one uses rates.