Thursday, July 6, 2017

Stack and unstack

My friend Geoff McGhee, who works for Stanford University's Bill Lane Center for the American West, has just published a nice series of interactive graphs and maps about California's move toward renewable energies. One of them caught my attention. Here's an animated GIF of it:

This is a nice example of a principle I explain in The Truthful Art: Stacked graphs show both the total and its components, but they emphasize the former, not the latter. When the total is more relevant than the parts, a stacked graph may be an appropriate choice.

However, what if seeing the variation of each portion with great accuracy is as important as the total? Then you need to let readers unstack the graph, or see each portion separately. Otherwise, estimating the variation of the parts not sitting on the horizontal baseline is hard.

Here's another example, a little classic by The New York Times.