Pie charts are evil.
They represent much of what is wrong with the poor design of many websites and software applications. They're also innefective, misleading, and innacurate. Using a pie chart as your graph of choice to visually display important statistics and information demonstrates either a lack of knowledge, laziness, or poor design skills.
Figure 1: A floating, tilted, 3D pie chart with shadow trying (poorly)to show usage statistics within a graphics application.
Of course, pie charts in and of themselves are not evil. This blog is really about designers making poor decisions for all the wrong reasons. In order for a pie chart to appear on a web page, somebody chose it over the other alternatives, and probably thought they were doing the right thing. They weren't. Using a pie chart is almost always a bad design decision.
Figure 2: Pie Chart from an Oracle Reports User Guide
A pie chart does not do the job of effectively displaying information in an elegant visual form. Being circular, they use up too much space while not allowing their labels to line up. Bar charts, line charts, and tables do a much better job. Expert designers, statisticians, and business analysts have documented their many failings, and strongly urge software and report designers not to use them. It's obvious to them that the pie chart has too many inherent defects to ever be used effectively.
Figure 3: Demonstration of how comparing data between multiple pie charts is difficult.
Yet pie charts are still used frequently in today's software applications, financial reports, and websites, often on the opening page as a symbol of how the data inside is represented. In an attempt to get a flashy colorful graphic to break up boring text, designers will often settle for a pie chart that looks like pac man, a colored spinning wheel, or a 3D floating alien space ship.
Figure 4: Best use of a pie chart I've found yet.
Why is the pie chart so popular? Through its constant use and iconic representation as the classic chart, the idea persists that it must be a good choice, since everyone else is still using it. Like a virus or an urban legend, no amount of vaccine or debunking will slow down the use of pie charts, which seem to be resistant to logic and common sense. Even the new iPad from Apple showcases the pie chart as one of its options.
Figure 5: Screen shot of new iPad showcasing pie charts.
Regardless of the futility in trying to rid the planet of this often used poor design choice, I now present to you my top 10 reasons why you should never, ever user a pie chart again.
Number 10 - Pie Charts Just Don't Work When Comparing Data
Number 9 - You Have A Better Option: The Sorted Horizontal Bar Chart
Number 8 - The Pie Chart is Always Round
Number 7 - Some Genius Will Make It 3D
Number 6 - Legends and Labels are Hard to Align and Read
Number 5 - Nobody Has Ever Made a Critical Decision Using a Pie Chart
Number 4 - It Doesn't Scale Well to More Than 2 Items
Number 3 - A Pie Chart Causes Distortions and Errors
Number 2 - Everyone Else Uses Them: Debunking the "Urban Legend" of Pie Charts
Number 1 - Pie Charts Make You Look Stupid and Lazy
