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January 06, 2012


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This map has a major problem with the color palette--it is difficult to pick a county on the map and then look up the value in the scale. This is due the HCL color scale.

The reason HCL colorspaces are perceptually uniform is because they are perceptually indistinct. Seems like a no-brainer that if you can't tell the difference between colors then you can't read values off a map.

Perceptually uniform HCL colorspaces have some theoretical justification and have gained popularity, but their application in real graphics demonstrates significant problems.


While this particular set of data demonstrates a problem, I don't know that HCL is the issue. The issue here is that the data are/is congested to the middle of the scale, so we get mostly one step color boundaries at the middle of the scale. I don't know: is that particular to HCL? I suspect the same would happen with any scale.

The resulting response in the eye/brain is appropriate: WTF happened, there's no difference!!! To that extent (which is what matters), the graphic is successful.

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