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Your Pie Chart Questions Answered here

our Pie Chart Questions Answered here

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.

Comparing a Pie Chart and a Column Chart
Comparing a Pie Chart and a Column Chart

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.

Pie Chart Showing Percentage of Profit Contributions
Pie Chart Showing Percentage of Profit Contributions

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.

Comparing the Effectiveness of Communicating Proportional Data in a Column Chart vs. a Pie Chart
Comparing the Effectiveness of Communicating Proportional Data in a Column Chart vs. a Pie Chart

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 Similarly Sized Data Values
Comparing Similarly Sized Data Values

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.

Comparing Data over Time in Pie Charts vs. a Line Chart
Comparing Data over Time in Pie Charts vs. a Line Chart

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.

A Pie Chart with Too Many Slices
A Pie Chart with Too Many Slices

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%).

Pie Chart with a Clearly Noticeable 25% Category
Pie Chart with a Clearly Noticeable 25% Category

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.

Pie Chart with a Difficult to See 25% Category
Pie Chart with a Difficult to See 25% Category

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.

3D Pie Chart
3D Pie Chart

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.

Pie Chart with Legend
Pie Chart with Legend
Pie Chart with Category Labels
Pie Chart with Category Labels

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.

Pie Charts with Similar (Left) and Distinct (Right) Colors
Pie Charts with Similar (Left) and Distinct (Right) Colors

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 additional tips or warnings about pie charts, please post your feedback as comments in this blog.

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