Problems with pie charts There seems to be in increasing discussion about pie charts. 
The main arguments against it seem to be:


*

*Area is perceived with less power than length.

*Pie charts have very low data-point-to-pixel ratio


However, I think they can be somehow useful when portraying proportions. I agree to use a table in most cases but when you are writing a business report and you've just included hundreds of tables why not having a pie chart?
I'm curious about what the community thinks about this topic. Further references are welcome.
I include a couple of links:


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*http://www.juiceanalytics.com/writing/the-problem-with-pie-charts/

*http://www.usf.uni-osnabrueck.de/~breiter/tools/piechart/warning.en.html

In order to conclude this question I decided to build an example of pie-chart vs waffle-chart. 

 A: My personal problem with pie charts is while they may be useful to show differences like this: 

way too many people use it to show that:

A: I wouldn't say there's an increasing interest or debate about the use of pie charts. They are just found everywhere on the web and in so-called "predictive analytic" solutions. 
I guess you know Tufte's work (he also discussed the use of multiple pie charts), but more funny is the fact that the second chapter of Wilkinson's Grammar of Graphics starts with "How to make a pie chart?".
You're probably also aware that Cleveland's dotplot, or even a barchart, will convey much more precise information. The problem seems to really stem from the way our visual system is able to deal with spatial information. It is even quoted in the R software; from the on-line help for pie, 

Cleveland (1985), page 264: “Data that
  can be shown by pie charts always can
  be shown by a dot chart.  This means
  that judgements of position along a
  common scale can be made instead of
  the less accurate angle judgements.”
  This statement is based on the
  empirical investigations of Cleveland
  and McGill as well as investigations
  by perceptual psychologists.
Cleveland, W. S. (1985) The elements
  of graphing data. Wadsworth:
  Monterey, CA, USA.

There are variations of pie charts (e.g., donut-like charts) that all raise the same problems: We are not good at evaluating angle and area. Even the ones used in "corrgram", as described in Friendly, Corrgrams: Exploratory displays for correlation matrices, American Statistician (2002) 56:316, are hard to read, IMHO.
At some point, however, I wondered whether they might still be useful, for example (1) displaying two classes is fine but increasing the number of categories generally worsen the reading (especially with strong imbalance between %), (2) relative judgments are better than absolute ones, that is displaying two pie charts side by side should favor a better appreciation of the results than a simple estimate from, say a pie chart mixing all results (e.g. a two-way cross-classification table). Incidentally, I asked a similar question to Hadley Wickham who kindly pointed me to the following articles:


*

*Spence, I. (2005). No Humble Pie: The Origins and Usage of a Statistical Chart. Journal of Educational and Behavioral Statistics, 30(4), 353–368.

*Heer, J. and Bostock, M. (2010). Crowdsourcing Graphical Perception: Using Mechanical Turk to Assess Visualization Design. CHI 2010, April 10–15, 2010, Atlanta, Georgia, USA.


In sum, I think they are just good for grossly depicting the distribution of 2 to 3 classes (I use them, from time to time, to show the distribution of males and females in a sample on top of an histogram of ages), but they must be accompanied by relative frequencies or counts for being really informative. A table would still do a better job since you can add margins, and go beyond 2-way classifications.
Finally, there are alternative displays that are built upon the idea of pie chart. I can think of square pie or waffle chart, described by Robert Kosara in Understanding Pie Charts.
A: Pie charts, like pie, may be delicious but they are not nutritious.
In addition to points made already, one is that rotating a pie chart changes perception of the size of the angles, as does changing the color.
If a pie chart has only a few categories, make a table.  If it has a LOT of categories, then the slices will be too thin to see (much less to label accurately).
I wrote about this on my blog.  A link via the wayback machine.
A: I think you've answered your own question for the 2nd bullet point. If you want to take up valuable real estate, so be it!  However the first bullet is more important.  With a bar chart the observer needs to estimate relative proportion based upon only 1 axis.  With a pie chart judging along at least 2 axes are involved. And one axis is curved.
I think that pie charts are used most effectively when you have many categories in the pie, with a legend,  and it is not all that important to judge proportion.
A: I can think of almost no case in which a pie chart is better than a bar chart or stacked bar if you want to convey information.
I do have a theory or two on how pie charts got to be so popular.  My first thought is related to PC commercials. Early PCs had text screens (24 x 80 characters), often green like old mainframe CRTs. To show off the new graphics screens that had a Red-Green-Blue pixel basis, a pie chart was ideal. A text screen could do a bar chart after a fashion, but couldn't do a remotely credible pie chart.  Pie charts looked a lot more serious than showing a Mario Brothers screen, regardless of how the PC would actually be used. Thus, it seemed like every PC commercial in the late 1980s and early 1990s showed a pie chart on the monitor.  
A second theory is that a bar chart or stacked bar is better if you want to convey information. But what if you don't? Then a pie chart works -- and charts with 3-D effects work even better.
A: Your waffle chart needs the red and blue values switched. As to the question of pie vs waffle, I lean toward waffle. With waffle charts you can still get the information across at small sizes even if the blocks blend together, the color still represents the regions.
