Pie Chart Do's and Don'ts - A Pi Day Tribute (March 14th)
In honor of Pi Day, Cullen Keeter has put together four critical do's and don'ts about pie charts. Check out this quick read and take your data presentation skills to the next level!
Many people have come to the conclusion that pie charts are worthless and a terrible waste of space when presenting data, and thus should never be used. I disagree with that sentiment. Pie charts can be extremely useful when used correctly and sparingly!
Now, let’s be clear on this right from the start: in today’s data landscape, pie charts are incredibly overused and misused. However, that doesn’t mean that they cannot be extremely useful when done well. We will not discuss the design aspects, like using a 3-D view (never do that, by the way) or using color to emphasize importance or direct your audience’s attention. We’re going to keep our focus strictly on the technical aspects of pie charts.
So, what are some general rules when using pie charts? Glad you asked.
1. Use it to show parts of a whole
2. Limit it to just a few variables
3. Only use one at a time
3.14 Focus on only one time-period
Showing parts of a whole with pie charts is a great way to easily call attention to specific parts.
This can help show high or low leverage. Percentages are also a great thing to show using pie charts as parts of the whole. Many people have started to utilize bar charts to compare percentages, and this is a great example of both options being a good choice, depending on the story you are trying to tell.
While both options show the high percentage of ‘Part 3’ when compared to the other three items, the bar chart better shows how much higher Part 3 is in comparison, and the Pie Chart shows how much of the whole is filled by Part 3.
Pie charts need to be limited to just a few variables.
Often you see a pie chart with 15 - 20 different slices. This just makes it unreadable. The reader spends too much time searching for the slice you care about, or figuring out which parts are bigger than the rest.
By limiting the number of variables, you are able to easily find and compare them to the other slices. A generally accepted maximum number of variables is 5, but it's even better if you can stay below 4.
When dealing with a large number of variables, try to think about the parts of a whole. Instead of having 15 slices, why not highlight the 3 you are trying to bring attention to, then group the rest as ‘other’. This encompasses the full picture, but also limits the cluster caused by having many variables.
If a visualization is going to require more than 1 pie chart to fully understand the story, don’t use a pie chart.
There are so many other charts that we can use. This is especially true when trying to compare things.
Stacked bar or column charts are a much better choice here. Having pie charts next to each other to compare can make it very difficult to see differences. You can barely tell a difference between Department A & C, and with Department B between them, it becomes even more difficult.
Do not use them for comparing variables over time.
Similar to only using one pie chart at a time, when you are looking at things over time you want to compare apples to apples. This is very difficult to do when looking at two pie charts next to each other. There are much better options to compare things over time. A bar or column chart works great here, or even a line chart! Pie charts in this situation creates confusion and makes accurate data difficult to gather. Use pie charts so show a snapshot rather than a time series.