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?