Pie charts are one of the most common yet misunderstood forms of data visualization. Since March 14 is National Pi(e) Day, we thought we’d take a few moments to help both new and experienced data visualizers alike understand how to use one of our favorite desserts – Er, charts – effectively.
Pie Chart Mishaps and How to Avoid Them
Simply put, pie charts are best used to show parts of a whole. Specifically, pie charts should illustrate meaningful relationships between percentages, or parts of 100%. If the data you want to display doesn’t add up to 100%, a pie chart might not be your best choice. Here are some of the most basic pie chart rules:
- Don’t use pie charts if your data involves time. If you want to show how a specific metric has changed over time, avoid the pie chart. Pie charts are static. In other words, they don’t have an axis you can label with dates. Because people tend to visualize time in a linear fashion, it’s difficult to communicate time with a circular chart.
- Don’t use pie charts if you have too many slices. Sure, you might be able to get a dozen slices from a real pie, but pie charts are most effective when used to display only a few items. The goal of a pie chart is to give users a glimpse of information quickly. If your data starts to look cluttered in a pie chart, you may have bit off more than you can chew.
- Don’t use too many labels. As a rule of thumb, avoid labeling your pie chart – with the exception of a color-coded key displayed at the side. While your data may seem more precise with labels, you also run the risk of confusing viewers. Generally speaking, the less time you need to decipher a graph, the better.
The Perfect Recipe for an Effective Pie Chart
When used correctly, pie charts can be powerful. Because they’re so easy to grasp in a short amount of time, you can convey big ideas with only a few lines. Let’s say you wanted to demonstrate the profitability of four companies: Company A, Company B, Company C, and Company D. By inputting this information into a pie chart, you can see the value of each company at a glance, identify the most profitable one, and spot potential underperformers.
Read next: Top Charts & Graphs for Your Data
A few secret ingredients to make your pie chart easy to read:
- Keep the color-scheme flat. While the tones of each slice should be easy to differentiate, it’s important to avoid any decorations that could interfere, such as highlights, shadows, and gradients.
- Two-dimensional is better. You might be tempted to make your pie chart 3D, but this can skew the relationship between the slices. When in doubt, keep it simple and stick to a 2D graph instead.
- Organize your data. Because people tend to read pie charts clockwise, it’s usually most effective to put the largest slice at the top, then disperse rest of data around the chart so that each slice displays a smaller percentage than the last.
- Use six categories or fewer. While there isn’t a hard-and-fast number of categories that work or don’t work for a pie chart, six is a pretty safe amount. The more categories you need to display, the longer it will take your audience to understand them.While there isn’t a hard-and-fast number that works or doesn't for a #piechart, six is safe. #dataviz Click To Tweet
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