It can be quite confusing when choosing a chart to represent your data. Perhaps the data is quite complex and choosing the wrong chart may lead to misinterpretation of the data. This blog will answer your common questions related to using pie chart:
- What is a pie chart?
- When to use a pie chart
- When not to use pie charts
- Best practices in using pie charts
At the end of this blog you will know when to choose pie charts to represent data.
What Is a Pie Chart?
A pie chart is a circular chart that partitions the circle into slices, where each slice represents part of the whole or a percentage of the total. Pie charts help show decisive quantitative comparisons using size, angles, areas, and arcs of the circle.
When to Use a Pie Chart
Pie charts are best used when you want to compare data in a way that is visually pleasant. If you have categorical data, especially nominal or ordinal categories, then using a pie chart would work well, as each slice can represent a different category.
Pie charts should be preferred only if you have one set of data. In a pie chart, each category is a proportion of 100 percent. Using negative values or zero values, such as in bar charts, can be complicated.
Simplicity with One Bigger Slice
Pie charts are more effective than bar charts at showing specific part-to-whole comparisons. In the following charts, you can quickly notice that the pie chart shows segment A is half of the pie. But it is not easy to make this distinction in the bar chart. Pie charts are useful for showing simple distributions with one slice bigger and others smaller, because it easily conveys the story of the data.
Percentage of Total
Pie charts display the percentage of a total. The following chart shows the profit of each state, which sums up to 100%. Pie charts won’t suit situations that require plotting error bars (such as 95% confidence intervals). So, if your data sums up to 100%, you should choose a pie chart.
Most of the time, it is difficult to identify a sum up to 100% in a bar or column chart compared to a pie chart. In the following figure, the pie chart quickly communicates a story to the viewer.
When Not to Use a Pie Chart
Comparing Slice Sizes
It is very time consuming and tough for the human brain to compare the size of one part of a pie chart to another, especially when the slices are not adjacent to each other and are similar in size. In such scenarios, you should try either a column or a bar chart.
In the following figure, the comparison using the bar chart is much better than the pie chart.
Comparing Two or More Data Sets
It is not recommended to use pie charts to compare two or more data sets (especially for comparisons over time), since it would be very difficult to compare the size of slices between pies. For this situation, we recommend using a line chart or area chart to quickly view and compare the changes. The following image shows the difference in comparing data over time between pie charts and line charts.
Too Many Slices
You should always consider the maximum limits of using categories or slices in your pie. A best practice is to have a maximum of 4–6 categories, or else it becomes difficult for the reader to determine the size between each segment. If the number of categories exceeds 6 slices, perhaps you should consider another chart type.
In the following pie chart, the reader would have to make a lot of minute comparisons between each slice to determine which one is the biggest.
Best Practices in Using Pie Charts
Positioning the Pie Chart
How a pie chart is rotated and positioned plays a vital role in showcasing its data. For instance, consider the following chart. This pie chart clearly communicates to the reader that the green slice occupies one quarter of the pie (25%).
Now look at the following pie chart. In this case, it is not so easy to notice that the green slice is one quarter of the pie. But this chart is same as the previous chart; it is just rotated slightly. For a pie chart, slight position changes can make a significant difference in the reader’s perception.
Don’t Use 3D Pie Charts
3D pie charts can be misleading, causing readers to make wrong decisions. When glancing at a 3D pie chart, slices in the front will look bigger than slices in the rear, even when front slices are literally smaller. This easily leads to wrong interpretation of the data by the viewer.
Remove the Legend
Another issue with pie charts is the usage of legends. In the following chart, the reader’s eyes would navigate back and forth between the chart and legend many times to read it.
In this situation, it is best to repurpose the legend as category labels placed on the pie chart itself for quick readability.
Use a Variety of Colors
Considering a maximum of 6 categories, make sure to choose different colors for the pie chart so each slice is easy to distinguish. Don’t pick colors that are the same or too similar. They will be too difficult to compare.
Conclusion
Hopefully this blog has helped you get a clearer idea of pie charts, when and where they should be used, and best practices in using them. The goal of any chart is to convey a proper story to the viewer in a single glance, to help the viewer understand the pre-defined decisions that we planned to convey. Use charts and other tools wisely to develop attractive and informative dashboards with ease using Bold BI.
If you have any questions on this blog, please feel free to post them in the following comment section. To get started with Bold BI, please request a free 30-minute demo with our experts to discuss creating dashboards and any other features you would like to learn more about. You can also contact us by submitting your questions through the Bold BI website or, if you already have an account, you can log in to submit your support question.
Originally published at https://www.boldbi.com on June 21, 2019.
