Despite the overwhelming evidence proving pie charts ineffectively display data, designers continue to use this deficient graphic. Two of the most prominent data visualization experts, Stephen Few and Edward Tufte, both agree that the usefulness of the pie chart is limited.
“Of all the graphs that play major roles in the lexicon of quantitative communication,” Few maintains, “the pie chart is by far the least effective.” Edward Tufte is even more blunt. In The Visual Display of Quantitative Information, he wrote, “Given their low data-density and failure to order numbers along a visual dimension, pie charts should never be used.”
And yet we continue to find pie charts everywhere. Recently, on /r/dataisbeautiful, this pie chart made it to the front page. The chart has several deficiencies, including the desaturated and nearly monochromatic color scheme, but its biggest flaw is its use of the 3D option. As flawed as pie charts already are, the use of an unnecessary third dimension makes its problems substantially worse.
Below I reveal exactly how much using 3D distorts the data displayed in the chart. On the left, I modified the original pie chart by increasing the color contrast to make the slices easier to differentiate. On the right, I created a 2D pie chart that more accurately displays the same data. I labeled the angle of each slice in blue. As the annotations show, both charts are not the same. For instance, the angle of slice 4 on the 3D pie chart should be almost twice as big, while slice 7 has the opposite problem. The angle of slice 7 should be around 50% smaller than it actually is.
information designers Giorgia Lupi and Stefanie Posavec visualize the mundane details of their daily lives in magical illustrated postcards they mail to each other across the Atlantic in a heartwarming yearlong correspondence project. More here.