Visualizing Proportions - Data Points: Visualization That Means Something - page 163

continues to rise. As a result, the percentage of the population in older age
brackets has increased. By how much has this age distribution changed over
the years? Data from the U.S. Census Bureau can help you see via a stacked
area chart. You want to see how the proportion of older age groups has
increased and how the proportion of the younger age groups has decreased.

You can do this in a variety of ways, but
first use Illustrator. For the stacked area
graph, it comes in the form of the Area
Graph tool (Figure 5-21).

Click and drag somewhere on a new
document, and enter the data in the
spreadsheet that pops up. You're famil-
iar with the load data, generate graphic,
and refine process now, right?

FIGurE 5-21 Area Graph Tool

You can see a stacked area chart, as
shown in Figure 5-22, after you enter
the data.

FIGurE 5-22 Default stacked area chart in Illustrator

The top area goes above the 100 percent line. This happened because
the stacked area graph is not just for normalized proportions or a set of
values that add up to 100 percent. It can also be used for raw values, so
if you want each time slice to add up to 100 percent, you need to normal-
ize the data. The above image was actually from a mistake on my part; I
entered the data incorrectly. Oops. A quick fix, and you can see the graph