I left a comment on Eric Fischer’s photoset laying out some of my thoughts on the coloring of his urban racial/ethnic distribution maps, to which he had the following response:
Thanks for trying out some other colors! To my (red-green-colorblind) eyes, the darker green does make for much better contrast with orange, but becomes hard to tell from red. I want to try it again with colors chosen from from the “Colorblind barrier-free color palette” and see how well that seems to work.
Here’s an image from the link he provided that gives a nice illustration of how colorblindness can present a challenge to the delivery of information through color.
When you lose one type of cone cell, it drastically reduces your ability to discern between some colors and puts a pretty severe limit on the tools that a cartographer or graphic artist seeking to reach a color blind audience.
I know that in my biggest foray into map making during the 2008 presidential primaries used a coloration scheme that was heavily dependent on the viewer’s ability to discern between colors across the spectrum. The one saving grace of my democratic primary map is that the third place candidate, John Edwards, dropped out of the race early on and didn’t leave much of an impact and thus there isn’t much green on the map.
Moving to a different, though related matter, Phil, whose comment at Andrew Gelman’s blog I referenced in my last post left a comment in return that touches on many potential avenues of exploration, but I want to emphasize just one part of the comment for now:
To some extent you/we are reinventing the wheel: I know I have seen work from at least fifteen years ago (maybe by researchers at IBM?) about how to design graphics so that different colors have equal visual weight, and also research on how to create intensity or saturation scales that people perceive as linear. Perhaps some searching on the intertubes would turn up the work I’m thinking of, and doubtless a lot of related research as well. Whatever you (or we) discover is going to turn out to be “well known” to the kind of people who know this kind of thing well.
My experience with map coloration consists mainly from my experience as a consumer of maps and the time I spent making the primary maps. While I do think that my experience was valuable and has given me a few insights on the matter, there is a vast literature of information that is now at my fingertips because of the Internet and I’ve barely scratched it.
Expect more comments from me on this matter. I’d love to see how the information available informs my experiences in 2008 as well as their applicability to maps like Fischer’s.