Data Viz Done Right

September 13, 2010

Energy Generated by a Pie

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Our power company, Cobb EMC, sends out a monthly community magazine and it always provides nice stories on how they support the community and how they utilize their energy resources.

In the September edition of Georgia Magazine, they published a pie chart of the fuel sources of energy generated (see p. 15).



When I first looked at this I thought Coal was the #1 fuel source. Why? Because Coal was on the top of the pie and it just looks like it was the largest. Fortunately there are labels that let me know otherwise. If I was forced to use a pie chart (i.e., if the purpose was to establish a parts-to-whole relationship), I would present it like this:



Some improvements include:
  1. Displaying the data largest to smallest starting at the 0 degree mark.

    This allows you to quickly see that a great, great majority of the fuel comes from two sources. It's much harder to see in their pie chart.

  2. The 3D view has been removed.

  3. The spaces between the slices have been removed.


If I were to present this data, I would present it in a ranking relationship with a bar chart. I would want to convey to the reader the fuel sources that provide the most energy, not necessarily the contribution to the total.



To me, it's much easier and quicker with the bar chart to see how much more energy comes from nuclear and coal than from natural gas and hydroelectric sources. I'm going to write to the editor.

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