Pie Chart Rant #2: 3D is a nightmare
I’ve run into a lot of pie charts that are tilted, so that they appear to be a thick disk, as viewed at an angle. I think this effect is used so that it will look cool, because I can’t imagine any other reason to use it. Here is an example:
Tilting a pie chart makes it harder to read.
So what’s wrong with this? Well, the whole point of a pie chart is to convey percentage. So, is the blue wedge more or less than half of the pie chart? It’s hard to tell because when the chart is tilted at an angle, there’s distortion of the chart. Things further away get smaller, things closer get bigger and as a result, the wedges are distorted. So it makes it more difficult to read the chart.
Here’s another example:
This pie chart is tilted - and it has too many wedges.
As you know, I don’t advise using pie charts with more than five wedges, and this is another good example of why. Can you tell, by looking at this, which wedge is the largest? The smallest? It’s impossible to parse this information. The pie chart is really obscuring the data, not revealing it. The best that we can say after looking at this graph is that all the wedges are approximately equal. Not very useful.
Here’s another example:
Another tilted pie chart
Here’s the same chart, in 2 dimensions.
The same chart, in 2 dimensions
As you can see, it’s much easier to read and, I think, looks better too. So, when you have to use a pie chart, keep it 2-dimensional.
What do you think? Is there ever a reason to use this 3D effect?
| Category: Rant | 3 comments » |
January 10th, 2010 at 10:22 pm
Hagan, in principle the only reason to give the pie chart depth would be the need to assign a variable to that dimension. In that case, the depth and volume of each slice would carry meaning.
But the complications of the perspective view would still give a distorted sense of the relative dimensions and volume of each slice. So a tilted pie chart is still a poor choice.
Unfortunately, when the user chooses to display data as a pie chart, both Microsoft Office products and Corel Office Suite products produce a tilted pie chart by default. You can turn the depth off, but it shouldn’t be there to begin with. After all, there really is never a good reason to use a 3D pie chart.
January 15th, 2010 at 11:31 am
Great comments, Cliff… I suppose you could add information into the 3rd dimension of the pie chart (the thickness of the slice indicating something else), but I agree – the complications of the perspective view will make that information distorted as well – in fact, obscured. The front of the pie will make the back of the pie impossible to properly see (unless it’s translucent? Ugh). I find it impossible to imagine a 3-dimensional pie chart that actually pulls that off. But I readily admit that my imagination may not be up to the job!
As for Office and Corel, it does seem that they’ve gone out of their way to make the default charts 3-dimensional … but all of the examples I’ve shown are from web applications, where more choice is available. I suspect those teams just copied what they see in Office, assuming that it must be right. This is why I think all companies in leadership positions must really give UI their extra effort – so many people copy what they do!
January 29th, 2010 at 1:20 pm
Just because you can, doesn’t mean you should.
Web apps are about getting the data you need to complete your work and not about, “Oh, whoa! Cool! Hey Bob, check out this nifty 3d-chart.” Pretty sure no one goes home to show their family and friends a web app with 3d charts.
So, I’m on board. 3d charts provide no extra value and just increase visual noise.