For example, dividing the number of people in each tract by the number of households gives you the average number of people per household. Using ratios evens out differences between large and small areas or areas having many features and those having few, so the map more accurately shows the distribution of features. Map courtesy of CH2M HILL, Englewood, Colorado. Proportions and Densities Two special ratios are proportions and densities. Proportions show you what part of a total each value is.
Densities show the distribution of features or values per unit area.
For example, by dividing the population of a county by its land area in square miles, you get a value for people per square mile. That is important to realize, because knowing how the values are distributed between the highest and lowest values will help you decide how to group them for presentation, so you can see the patterns.