Representing Data - Data Points: Visualization That Means Something - page 453

mistake seems to come up occasionally. Sometimes it's due to mislabeling,
but some people just aren't familiar with the concept.

F I G U R E 3-17 Incorrect
and correct pie charts

Categorical
Data doesn't always need to be numeric. It can be cate-
gorical, such as people's cities of residence or the polit-
ical parties of government officials. A categorical scale
provides visual separation for these different groups and
often works with a numeric scale. A bar plot for example,
can use a categorical scale on the horizontal axis and a
numeric scale on the vertical to show counts or mea-
surements for different groups, as shown in Figure 3-18.

Spacing between each category is arbitrary because
it does not depend on a numeric value, but it is typi-
cally adjusted to increase clarity, which is discussed in
Chapter 6, “Visualizing with Clarity.”

FIGUR E 3-18 Numeric and categorical scales on a bar plot

Ordering should be used in the context of the data.
Although this can also be arbitrary, for an ordinal scale
that uses categories, order of course matters. If your data is a categorical
ranking on movies that ranges from horrible to great, then it makes sense to
keep that order visually, which makes it easier to compare and judge quality.