Jumping Into Visualization Without the Math
October 16, 2009
I found this link from Instapundit, so credit where it is due.
You may have seen this visual of job loss across the country. It maps the job gains and losses in major metro areas across the country and, on the surface it seems pretty cool. Here’s October 2008.
As someone who really loves information visualization, I applaud the effort. But it’s wrong.
Let’s take a quick look at the legend. See if you can spot the problem.
Keen readers will notice the problem… whoever created this visual scaled only the diameter of the circle. The problem with this is what we can see below.
Here I took the “10,000” circle and duplicated it over 50 times within the “100,000” circle. If this visual were an accurate one, we would multiply the 10,000 circle ten times to get 100,000. That’s just the way these things should work.
Math Time! (skip if you don’t care)
The area of a circle is calculated with the equation:
Which means that when they increase the height of the circle by 10, they increase it’s area by 100. This means that instead of the numbers increasing the way they should, the small numbers end up looking REALLY small and the big ones look absurdly huge.
End of Math Time
I’m not trying to be an a**hole here. The idea behind the visual was a good one. But these things really do need to be accurate. Most people don’t know how to tell when a visual is in error and they end up with an incorrect impression from a poorly built infographic.