Pie chart has its uses
Published on 2023-03-18 11:26
Pie chart is a chart that people in data visualization fields love to hate. It is basically a Comic Sans of charts.
How people misuse it
Pie and doughnut chart tempting to use when we want to show all the parts in one. Unfortunately, that's not how human brains work. We are not equiped to read and compare circular objects. Below are two examples of a pie chart. The first one has six similar values. Because of the lack of grid in bar chart it's hard to tell its values and accompanying table is necessary.
In the second example there are also six values. This time some values are the same and in general they are not as close in their values. In this chart it is hard to tell which is bigger with exception of the light blue segment.
How to actually use it
The most obvious use case is with pizza. Pizza is usually circular and when you take a look at it, you can easily estimate if you have enough or not. This applies to other foods shaped as a circle.
Second use when it's good to use a pie chart is from Prague's map of recyclables collection points. The map is full off small pie charts indicating which what types can be dropped off there.
One thing that I would like to see improved on the map is use of legend.
What to use instead
Instead of a pie chart we have several option. When we want to make it easy to compare bar chart is the most obvious solution.
Alternatively when we want to show proportions, we can use stacked bar chart. It's more readable for people because it is easier to compare two rectangles than two pieces of pie.
When you are picking a chart, please, choose the one that's boring and readable. In case of pizza, it's already eatable.