[codementum]

You're absolutely right. Everyone harps on pie charts for being awful for element-to-element comparisons. This mainly stems from Tufte's work and experiments from Cleveland and McGill.

However, in part-to-whole relationship tasks, pie charts can outperform bar charts, since in bar charts there is no true "whole".

(In addition to Few's post, Kosara has more on this: http://eagereyes.org/criticism/in-defense-of-pie-charts)

[cpeterso]

A composite bar chart is like a pie chart that has been unrolled. The length of the bar is the "whole".

http://www.ncsu.edu/labwrite/res/gh/gh-bargraph.html#composi...