Visualizing proportions using pie charts

The Pie Chart visualization is useful for showing simple proportions for a limited number of variables. If you have four values to compare, then the familiar pie slices can be a powerful visual aid. Increase to ten values of near-equal proportion, and you lose the audience. The slices must also be mutually exclusive and add up to a meaningful whole, such as 100 percent. The popular media are guilty of presenting opinion poll pie charts that add up to more than 100 percent.

Also, because the proportions are determined by angles and triangular section areas, people have difficulty accurately estimating the proportions, especially when they are close. Therefore, pie charts are almost always labeled with numbers. There is an excellent article at http://eagereyes.org/techniques/pie-charts on the advantages and limitations of the pie chart.

Let's look at the pie chart in Spotfire.

The data we'll use here is BaseballPlayerData.xls, which you can download from...