Given our natural construct of how we read a clock, it’s fairly easy to tell that Product A makes up roughly a quarter of total revenue and that Products A, B, and C combined are roughly two-thirds of total revenue. Suppose we want to focus on how much revenue a given product-or set of products-contributes to the total. Our sales example supports the first use case. To convey that one segment of the total is relatively small or large. If you want your audience to have a general sense of the part-to-whole relationship in your data and comparing the precise sizes of the slices is less important. There are two primary use cases for a pie chart: When you hear “percent of…” or “part of…” that’s one indication a pie chart could meet your needs. Pie charts are probably better than any other visual for expressing a part-to-whole relationship. Which you choose is largely dependent on what you want your audience to see or do with the graph. Alternatively, I could have labeled each segment with the respective dollar amount. In this instance, I put the total dollar volume at the top and labeled each segment with the percent of the total. You can see the part-to-whole relationship of each product’s contribution to the total in the pie below. The sum of each individual product’s sales equals the total sales amount. Imagine you have a portfolio of five products and you measure sales (in millions of dollars) for each. You can read more about their research in an illustrated tour of the pie chart study results. Recent research by Robert Kosara and Drew Skau demonstrated that we read pie charts by area-or possibly in combination with arc length-which debunked some previously held beliefs that pies are read by angle. Each pie slice has three visual components: its central angle, area, and arc length. Here’s a brief overview of how we consume a pie. A pie chart provides us this comfort of a part-to-whole relationship. We like things to be whole-and understand how the respective pieces relate to the whole. Pies are perhaps so commonly used because, as Manuel Lima writes about in The Book of Circles, humans gravitate to circles as the universal symbol of unity, perfection, and infinity.
Each slice represents one component and all slices added together equal the whole. Imagine an actual pie (I’ll let you choose your favorite variety!).
How to identify whether your data is better served as something other than a pieĭesign tips for creating an effective pieĪ pie chart expresses a part-to-whole relationship in your data. The good news is they do have a proper use case and it’s easy to use them appropriately. They are also one of the most widely condemned and misused. Pie charts are one of the most common types of data visualizations.