Visualizing Proportions - Data Points: Visualization That Means Something - page 136

What to Look for in Proportions
For proportions you usually look for three things: maximum, minimum,
and the overall distribution. The first two are straightforward. Sort your
data from least to greatest, and pick the ends for your maximum and
minimum. If you were dealing with poll results, these could mean the
most popular and least popular answers from participants; or if you were
graphing calories from separate parts of a meal, you would see the big-
gest and smallest contributor to the overall calorie count.
You don't need a chart though to show you minimum and maximum. What
you are most interested in is the distribution of proportions. How does the
selection of one poll choice compare to the others? Are calories spread
evenly across fat, protein, and carbohydrates, or does one group domi-
nate? The following chart types can help you figure that out.
Parts of a Whole
This is proportions in their simplest form. You have a set of proportions
that add up to 1 or a set of percentages that add up to 100 percent. You
want to show the individual parts relative to the other parts but you also
want to maintain the sense of a whole.
The Pie
Pie charts are the old standby. You see them everywhere these days, from
business presentations to sites that use charts as a medium for jokes. The
first known pie chart was published by William Playfair, who also invented
the line graph and bar chart, in 1801. Smart guy.
You know how they work. As shown in Figure 5-1, you start with a circle,
which represents a whole, and then cut wedges, like you would a pie. each
wedge represents a part of the whole. Remember that last part, because
a lot of beginners make this mistake. The percentage of all the wedges
should add up to 100 percent. If the sum is anything else, you have done
something wrong.