Vitriolic Rant Redux — 3D Pie Charts
By Tim Wilson on in Data Visualization, Excel with No Comments
Pie charts are generally bad enough. Mainly, because they take a lot of real estate to provide pretty limited information. But, they do have their place. That place is showing the relative relationship of the parts of a whole when there is no time dimension.
3D pie charts, though, are simply horrid! They actually misrepresent the data and remove whatever instantaneous clarity that a flat pie chart provides.
In the pie chart above, Which product has the greatest portion of the whole?
Product B. That’s not too hard.
Which is greater, Product A or Product D?
Trick question. They’re the same. And, you probably figured that out. But, in order to do so, your brain had to undo the 3D effect, since when it comes to raw area shown, Product A is larger.
When asked a direct question like, “Which is greater, Product A or Product D,” this isn’t too hard to do. But, that’s not usually the approach of interpreting visual displays of data. Rather, the viewer looks at it and says, “What does this chart tell me?” In a 3D pie chart, your brain has to spend extra cycles doing the A vs. D comparison for every wedge in the pie. And it gets pretty hairy when you’ve got, say, 10 or more wedges. What’s happening is your brain has to go through a (subconscious, but real) effort to remove the 3D effect. That’s an effect that somebody else wasted brain cycles and effort on adding in the first place.
This is the sort of inefficiency that process improvement folk salivate over finding in a manufacturing environment: “Person A unwraps a widgetlet and then screws it on to a doohickey and sends it to the next station. Person B then unscrews the widgetlet, inserts a washer, and then screws it back on in the exact same spot.” Obviously, if Person A didn’t screw the widgetlet on in the first place, then the process would have two steps removed: Person A’s screwing on of the widgetlet and Person B’s unscrewing of it.
It’s the same deal with 3D pie charts.