Volume Graphs and Timeline Skews — Graphing Pitfalls

Below is a beautiful graph that uses images to convey a whole lot of information — this picture literally takes the place of a thousand words, probably more. But it also illustrates a common problem we encounter when the relative size of each “fuzzy ball” represents the relative data; in this case, the number of deaths caused by each virus.

The problem remains that a ball with twice the area or volume doesn’t look twice as big, like a bar on a graph would — not even in the second half of this graphic, which does a more accurate job of presenting relatively sized images. There, for example, the Black Death (bubonic plague) doesn’t look four times bigger than the Spanish flu, even though it probably is — we would have to calculate to comprehend the relationship. Placing the data labels beside each image was a very smart idea.

The bigger problem is seen in the top portion of this visual: while trying to show a timeline diminishing into the far distance, the relative size of the balls gets so skewed that Black Death (bubonic plague) looks half the size of Spanish flu, not four times larger!

This approach conveys a lot of information at a glance, and the colours are very engaging. Clearly, a choice was made to sacrifice the relative size in order to illustrate the timeline. That is an editorial decision best made with purpose, not incidentally, and is definitely never to be made in order to misrepresent data. (We have no reason to assume anything but good intentions, here. It does make a great example!)

The problem with area graphs and skewed views.
Click here to see the original.

This image comes to us via “Visualizing the History of Pandemics,” on the Visual Capitalist blog.


For more information on problems to watch for in numbers, check out Getting the Numbers Right, now available.

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