Sometimes we are interested in seeing values that have been divided by other values. The first set of values is said to be “normalized” by the second set of values. For example, if we were interested in population density of counties, we would be interested in the value of population divided by the area in which it resides. Or, as in the next step, we might want to display the ratio of females to males, so we would apply normalization.
____ 21. Normalize the number of females by the number of males, using the Layer Properties window, Symbology tab, and the Fields area. (Females goes into Value and Males goes into Normalization) Classify into seven classes using Jenks. With the labels tab, label the areas using the expression [FEMALES]/[MALES]. Look at the map. Notice that the labeling makes an unreadable mess of things, with ratios carried out to 14 decimal places.
Go back to the Labels tab and use the expression
Round ([FEMALES] / [MALES], 2)
which has the effect of rounding the ratios off to two decimal places, and should give you the result shown in Figure 6-17