Getting Maps Right for the Color-blind Naturalist

Rainbow at dusk near Tarcoles, Costa Rica, 17 February 2010. Photo by Richard Brewer

The January 2010 issue of The Auk published my review of the Atlas of Breeding Birds of Ontario, 2001-2005.  It’s a fine book. It may be a little heavy for some readers–it weighs more than seven pounds.

The next (April) issue of The Auk published a Letter to the Editor that made reference to the review.  The letter from Wayne E. Thogmartin (with the U.S. Geological Survey at its LaCrosse, Wisconsin, center) was prompted, he wrote, by “a peculiar aside proffered by the author.”  He then quoted the following passage from my review:

A word about the colors of the maps:  Like nearly 10% of males in the United States (a similar prevalence in Canada, I suspect), I have red-green color blindness.  Though it may seem unfair that maps and other color-coded graphics should be designed with 10% of one-half of the human population in mind, I suggest that it is unwise to design materials that will be unintelligible or at best ambiguous for this segment of the population. My wife, like 99% of the female population, has good color vision.  She informs me that the breeding evidence maps use the following colors–gold, orange, red, yellow, and dark gray (plus white). I can separate all these colors, whether I can identify them or not.

I have more trouble with the relative abundance maps; they use white, yellow, gold, light orange, orange, and red.  In areas where the abundance level marches in orderly progression from low to high, I can pretty much distinguish the six abundance classes.  But an isolated blob might require considerable study in very good light.

At least these maps do not intermix red and green.

The emphasis was added by Thogmartin.

He calculated that at 8% prevalence in the general (male) population, about 140 members of the AOU are likely to have red-green color blindness, or “color-vision impairment.” He went on to say, “Any failure to produce a color legend that is informative to the full spectrum of ornithologists is unfortunate,” because methods are available that allow map-makers to produce maps with color schemes everyone can interpret. He cited several sources that can be consulted by the map-maker who aspires to inclusiveness and social equity.

I’m indebted to Thogmartin for making my aside operational.  I admit I’m puzzled by his characterization of it as “peculiar.”  But it does seem odd, if not peculiar, that one of the most important students of getting map colors right for the color-blind, as cited by Thogmartin, is also named Brewer.  That would be Cynthia A., professor of geography at Penn State (no relation).

Cynthia A.  has an online tool for map design, ColorBrewer, that looks very useful for designing color schemes. On the other hand, just having the cartographer confer with a color-vision impaired person might do the trick almost as well.  The map Presettlement Vegetation of Kalamazoo County, Michigan (Thomas W. Hodler, Richard Brewer, Lawrence G. Brewer (also no relation), and Henry A. Raup, 1981, Western Michigan University Department of Geography) has a color scheme anyone can readily interpret because a color-vision impaired person (me) chose the colors for the cartographer.

I noticed a couple of days ago that the National Weather Service’s on-line radar maps have a downloadable Color Blindness Tool (located on the left side of the screen under Additional Info:)  On-line radar has always looked like multicolored hash to me, so I’m hoping the tool (Visolve) will prove usable and useful.

2 thoughts on “Getting Maps Right for the Color-blind Naturalist

  1. Wayne Thogmartin

    I meant no disrespect when categorizing your comment on color-blindness in map-making. I found your comment peculiar only insofar as being ‘distinct from others’ – an observation of a personal nature that we rarely see within the confines of professional journals; had you not uttered it, I am certain I would continue making maps that were useful to me but clearly less useful to a sizable number of others. And for this reason, I am the indebted one.

  2. rbrewer

    @Wayne Thogmartin
    Glad you took my comment and ran with it. I should probably be indebted also to Todd Engstrom, book review editor for The Auk, for not holding me to the usual word limit. Bad colors for maps (and other diagrams) have annoyed me for a long time; as you point out very clearly, they are preventable. It’s a common problem elsewhere too. I just got a new Canon digital camera whose battery charger is red while charging and changes to green when fully charged (or so they say). My Nikon, which gave out, used blinking light for charging and solid light for charged–an easy solution but beyond Canon.

    Maybe I’ll become a red-green activist.

    Always glad to have contact with another Saluki (B.S., 1955), especially a zoological one.

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