Sunday, June 26, 2016

Diverging color schemes: Showing good data isn't enough; you need to show it well

Fraser Nelson, editor of The Spectator, claims that his map of Brexit is better than a diverging color scheme one. See his comparison:

I beg to disagree. Nelson's map is misleading and far from being “real”, although it does show accurate data. This is yet another example of how to build a dubious visualization using legitimate numbers. A much more truthful depiction of the results appeared in The New York Times (below). It improves on the imperfect binary Brexit map by adding shades of color, which is a great idea. Good data isn't the only component of visualization; the way you depict it matters a lot:

The Guardian used fewer shades of color, but it transformed the map into a cartogram. This emphasizes the relative weight of different regions of the country:

Actually, by taking a look at the maps by the Times and The Guardian, I'd argue that Nelson's article and map obscure the fact that the some highly populated areas of Scotland were strongly in favor of remaining in the EU.

UPDATE: On Twitter, Neil Richards wrote: “Made long comment on your blog but it got swallowed up! One point: red/blue not perfect because of political connotations. But yellow also indicates third party SNP these days. Any divergent palettes that don't include red, blue or yellow? 2/2.” I'd refer to ColorBrewer.

1 comment:

  1. Great post Alberto. I really like the diverging palette from the NY Times. The diverging palette works because there is a natural midpoint. The % of vote has a one-minus, meaning a 10% share of yes is a 90% share of no and 50/50 is a clear midpoint. You can calculate a one-minus for the % of unemployment, but in that case there is no natural midpoint (unless maybe someone is visualizing the optimal unemployment rate, below and above). If not using a diverging scheme, I think Mr. Nelson's map would work better as white to blue, rather than a mid-range blue to dark blue. The fact that there is such small variation in the color value makes this really problematic.