Bubble charts and their discontents II
More mischief in map coloring

Obesity bad, maps good

The recent coverage of obesity in the US media produced at least two very good data maps.  The New York Times printed this snapshot of the nation in 2004.


Because of a judiciously chosen color scheme, we can easily discern the pattern of obesity: more severe between the Lakes and the Gulf; least in the West and Northeast, especially in Colorado; quite bad in the middle and the South. Nyt_obesity_legend_1

The legend is deserving of much praise:   in defiance of popular but simplistic usage, the range was not divided into four equal parts (quartiles); rather, the designer selected four unequal parts so as to reveal the geographical pattern on the map. Besides, the complete range of the data was shown as is, where most would have artificially widened the range to 15.0% on one end and 30.0% on the other.

All in all, this is a simple graphic conveying a clear message.  Well done.

And yet -- the dynamic aspect of obesity growth alarms even more:

  • Within many states, more and more people are becoming obese
  • Nationally, more and more states have high obesity rates

These trends, along with others, are perfectly captured by the following terrific, dynamic data map, thanks to CDC.  It is a wonderful example of how the electronic medium (animated gif) can do wonders for the graphics designer. [You may need to click on the map to see the animation in a pop-up window.]

The time dimension is experienced rather than drawn on paper/screen.  This experience is in fact distorted, compressed time is what we feel, but the distortion improves rather than deter our ability to see trends.

  • The states between the Lakes and the Gulf led the nation throughout this period.
  • The ever expanding legend ingeniously draws attention to the fact that the worst states have gotten worse over time.
  • No single state has been spared: by 2001, only Colorado had an obesity rate below 15%; just 7 years earlier, in 1994, the entire Western half of the U.S. had obesity rates below 15%.

One small gripe: if read quickly, the reader can be forgiven for thinking that "white" indicates 0% obesity.  Not so!  "White" actually means "no data".  I'd prefer to use a neutral color for "no data"; when they started tracking, these states turned out to be no less obese than others.  By 1994, every state has started tracking obesity.

This dynamic map is really rich in information.  Feel free to leave comments about what else strikes you about it.

Reference: "Obesity Rate Is Nearly 25%, Group Said", New York Times, August 24, 2005; CDC Obesity Trends.


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Here's another way to view obesity patterns by state:


This is a funny chart that makes great use of scatter plots to reveal patterns.

I hope people don't take this chart too seriously because the joke is really on the non-obese people. Even in the most obese state, < 30% of the population are obese so the y-axis really reflects the non-obese people (not the obese as implied by the x-axis)!

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