I have worked on enterprise software (stuff behind the firewall) for many years, and whenever I’ve worked on data visualization – especially dashboards – religious arguments about the use of pie charts erupt.
In general, engineers, statisticians, and some designers find them abhorrent, shun them, and ridicule those who use or promote them. Edward Tufte finds them slightly less apocalyptic than PowerPoint, and Stephen Few argues in many articles about how pointless they are. They are difficult to read precisely, difficult to compare, and take up a lot of space for very little information display.
The other camp, generally product managers, marketing, sales folks, executives, analysts, and other business-focused folk request them and like them – sometimes in 3D or spinning. MBA educations, business magazines, analyst reports, and marketing brochures immerse these types of people in pie charts. They are part of the lingua franca of business. They communicate simple proportions of a whole quickly and attractively.
Myself, though I have affection for and intellectually lean toward Tufte and Few, I am a pragmatist and an agnostic when it comes to this choice. Yes, pie charts have many, many problems. And yes, many people like them.
Above all, I am committed to the UX mantra of “know thy user.” Who is the audience for this chart? Business folks who are extremely familiar and comforted by them? Then use them and prevent the question of “where are they?” Statisticians and scientists? Avoid them or risk having your product be ridiculed or dismissed.
If you find that pie charts are appropriate for your customers and users, then go ahead, toss that pie in Tufte’s face. But, please, if you must use one, design it well:
- A limited number of wedges, generally six or less, with the most important proportions of between 25% and 50%.
- Good color choice that emphasizes the important wedges.
- If precise values are needed, label each wedge or provide an accompanying table.
- Don’t use a pie chart if you want meaningful comparisons drawn or to show change over time.
- Avoid faux 3D effects.
- And, please, no spinning wheels-of-fortune.
Finally, realize that there are many – and many better – ways to communicate the same information. Information visualization is not a monotheistic religion. There are many gods in the pantheon, each of them with appropriate and inappropriate uses, beautiful and horrendous forms, useful and meaningless applications. Design from knowledge of the different types, not ignorance of all the others. Be a thoughtful acolyte, not a dogmatic sycophant.
UPDATE: Kathy Rowell chimes in.