Data Authors: Skilled Designers of Data Presentations - Data Fluency: Empowering Your Organization with Effective Data Communication - page 105

However, if you can understand how different charts address different types
of questions, you'll be well on your way to making good chart choices.

The first element in selecting charts is to understand that the purpose of a
chart is to make it easy for readers to identify patterns and see how values
compare to each other. The best charts maximize comprehension by playing
to the strengths of visual perception. People can judge values accurately on a
two-dimensional plane—the length of a line, the height of a bar, or the position
of a data point. Bar charts and line charts play to these strengths. The ability
to judge accurately declines when charts use other visual features to show
values—width, area, color intensity, and radial distance. Therefore pie charts
are generally less effective than bar charts because they require readers to
compare radial distances, as shown in Figure 5-17.

Unit Sales by Fruit Unit Sales by Fruit

80

Bananas

60

Blueberries Apples

40

20

Oranges

Pears

Apples Pears Oranges Blue-

berries

Bananas

F i g u r e 5 -17: Bar charts make it easier to compare values.

The second fundamental element in choosing charts is to know what you want
to show. There is no good answer to what is the right chart without knowing
the question you want to answer. The beauty of defining this question is that it
can reveal clues as to the chart you need to use. Take the following examples:

How do my sales break down by customer type?

⬛

What is the change in visitors over the last 3 months?

⬛

Which students have the best test scores and have improved
the most?

⬛