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.

JobLossOctober2008

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.

JobLossScale

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.

JobLossScaleProblem

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:

AreaText

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.

6 Responses to “Jumping Into Visualization Without the Math”

  1. Joshua Says:

    Exactly right! I took that graphic at face value (after noticing the data was really old) and wouldn’t have known. Thanks for pointing it out to us lay-people.

  2. Cameron Says:

    Two articles in 2 days? What’s going on here. I demand a two week wait period in between articles!

    Also,
    Good Catch.

  3. T. Jones Says:

    Hey brother, you have a typo in the last sentence — “built” not “build.” Delete the comment when you’re done. Keep up the good work.

    Jonesy


  4. Now we need someone to do a “re-do” and correct the mistake! I’m sure this information visualization has mislead a good percentage of the public.

  5. William Says:

    One point worth mentioning is that people do no perceive visual information in a mathematically accurate way. The images here scale linearly making the proportions seem inaccurately large. However, if the images of the circles scaled so that the area of the circles increased proportionately people would perceive the larger circles as being smaller than they actually are in comparison with the smaller circles. In other words, a 1.4×1.4 square does not appear to be twice as large as a 1×1 square, even though it is. Still, I do think that would be much less of a visual lie than scaling the circles linearly.

  6. Angela Says:

    Well, math aside, what you notice is that jobs are/were created in TEXAS and Washington, DC. Texas was largely untouched by the “crash” because they had already gotten their banking house in order after the savings and loan debacle. Plus, there’s still a “go get ’em” and self-reliance mentality there. The Washington jobs are just more expanding government. Excellent visual.


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