Monday, August 28, 2017

Shock and precision in visualization

Comparisons and context are at the core of data visualization. We humans have a hard time grasping large numbers, such as “9 trillion gallons of rain,” so transforming that magnitude into a pictorial illustration may help. Here's a graphic by The Washington Post; it's part of this story:

John Grimwade has a great collection of this kind of side-by-side pictorial comparisons. They surprise and illuminate, but they are quite limited. Sometimes it may be preferable to present data in a more abstract and precise manner, like this (h/t Sam Lillo):

Which graphics are better, the pictorial or the abstract? There is no better. It all depends on what your goals are. The former graphic is shocking, but it doesn't enable any analysis. Its power and its limitations reside in its bluntness. The latter lacks visual punch, but it's rich in detail.

No visualization is ever perfect, useful in every case and for every purpose, so the key to a successful data presentation is often to not limit yourself to just one graph, map or diagram, but to combine different kinds. The shocking ones work as a headline, pulling readers into the narrative by intriguing them; then, the more detailed ones provide some needed context and depth.

(The Washington Post has other graphics stories that are also worth your attention.)

UPDATE: Felix Salmon has just told me about a mistake in the copy of the first graphic. It reads “four miles square” when “four square miles” (the area of the base of the cube, 2*2 = 4) is more accurate. Felix adds: “just to be unambiguous: "four miles square" means a square with four-mile edges, i.e. 16 square miles.” In visualization, words are as important as visuals!

UPDATE 2: The Post has just corrected the graphic (see comment below)