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Raw vs. Ratio

 

The Case


The not very enlightening map.
source: Wired Magazine, April 2009
In Wired Magazine’s April issue there was a small map in their Rants section (letters to the editor) showing the number of Wired subscribers per state.

As a total map geek I was glad to see a map included but pretty quickly bummed out (as bummed as a tiny map in a magazine warrants anyway) to see that it was just the total number of subscribers.

California has lots of people in it.  So it stands to reason that it would also house lots of subscribers.  Same with Texas and New York.  Wyoming is our least populous state, so that fact that it also has the fewest number of subscribers is not surprising.  Or interesting.

 

A fellow geek, who is more motivated than I am, also noticed the relative lameness and wrote to Wired.  And Wired quickly replied with a "more illuminating take on the data."  Nice!

States of Confusion

I’m a bit of a data geek, so I was excited to see a map in the Rants section (issue 17.04). But the information is presented in such a way as to make it meaningless. The chart’s subtitle could be changed from "Wired Subscribers by State" to "US Population by State" without altering the picture a bit. (I should add that, out of all the issues of Wired I’ve read, this is the first time I’ve been less than 100 percent satisfied.)

Matthew S. Slafka
Kent, Washington


The totally awesome second-take.
source: Wired Magazine,
June 2009

Removing Enumeration Bias
In this follow-up version of the Wired subscribers map, we actually get a sense for how Wired-friendly the various states are.  A ratio of subscribers to population removes the bias of state population size.  So, now we see that Wyoming isn’t so dismissive as we thought and Texans aren’t necessary the avid Wired readers that we thought.

Thematic mapping has to break the world out into Enumeration Units -the chunks (in this case, states) that are assigned some visual variable (in this case, color).  Thematic mapping is almost always unfair.  We do our best to make the visualization as meaningful as possible, but the amount of stuff inside (folks living in California v. Wyoming) may vary greatly -and hose the message.  By making the wild card of population a denominator for the important stuff (subscribers) Wired made a ratio, mitigating the population bias and resulting in a much more illuminating story.

Communication
Maps and data visualizations in general are just distilled messages.  Just like gestures, speech, or paragraphs of text, visual graphics project a story.  Sometimes a raw count is what you want, sometimes a ratio is more informative.  Craft your visualization in a way that illustrates the truth of your data.

 

John Nelson / IDV Solutions / john.nelson@idvsolutions.com

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