The broken-out slice of the pie chart is badly distorted.
The slice is broken up into rings for each percentage, but the rings are sized by their width, not their area, so the areas are way off.
It says 57% Facebook. The width of the entire slice is 500 pixels, and Facebook's width is about 285 pixels - that's 57% of the width. But the area of the Facebook ring is obviously much greater than 57% of the entire slice.
In fact, since the area varies with the square of the radius, the inner rings all combined (43%) are only 18.5% of the area, and the Facebook ring is 81.5% of the area!
Or consider the two slices that are supposed to represent 13% each. The inner blue slice is 6.37% of the total area, and the red slice next to it is 8.88%. That's 40% bigger than the other slice that is supposed to represent the same amount.
Using widths that give correct areas would be misleading visually too, because the widths would then look wrong. Facebook's 57% would be only 34% of the width, and the inner rings combined would be 66% of the width.
I think the only way to fix this and stick with the pie representation would be to make the sections angles of the slice instead of rings within it.
For anyone who wants to make better charts by learning what not to do, I recommend the Junk Charts blog which picks apart all sorts of bad charts. I've learned a lot from it and it's entertaining too:
The slice is broken up into rings for each percentage, but the rings are sized by their width, not their area, so the areas are way off.
It says 57% Facebook. The width of the entire slice is 500 pixels, and Facebook's width is about 285 pixels - that's 57% of the width. But the area of the Facebook ring is obviously much greater than 57% of the entire slice.
In fact, since the area varies with the square of the radius, the inner rings all combined (43%) are only 18.5% of the area, and the Facebook ring is 81.5% of the area!
Or consider the two slices that are supposed to represent 13% each. The inner blue slice is 6.37% of the total area, and the red slice next to it is 8.88%. That's 40% bigger than the other slice that is supposed to represent the same amount.
Using widths that give correct areas would be misleading visually too, because the widths would then look wrong. Facebook's 57% would be only 34% of the width, and the inner rings combined would be 66% of the width.
I think the only way to fix this and stick with the pie representation would be to make the sections angles of the slice instead of rings within it.
For anyone who wants to make better charts by learning what not to do, I recommend the Junk Charts blog which picks apart all sorts of bad charts. I've learned a lot from it and it's entertaining too:
http://junkcharts.typepad.com/