I think it is a common misconception that visualization needs to be complicated to convey a number of variables, and the two examples that I have chosen address this issue. The first example is a UV index map from the EPA that is updated regularly on their website.
The bad:
There are a few features with the EPA’s UV index forecast that are worth pointing out. First, the color scheme is very misleading. We customarily associate red with danger and ‘cooler’ colors with safety. This map has the red hues squarely in the middle of the scale with blue tones encapsulating both ends of the spectrum. In fact, the two colors assigned to the lower and upper end of the scale are very similar and could almost be used interchangeably. There is no logical progression to the colors, and the map author would have been better off using saturation (with one hue) in order to show increased UV levels. (The full sized version can be seen here.)
The good:
This visualization shows the additional Crayon colors that have been created since 1903. Color is used to represent actual color, which could have been accomplished less dynamically a number of different ways. The timeline emphasizes the number of additions within the last 20 years, while showing the smaller proportion of changes before 1958. A table showing the same information would not show the diversity as effectively. (The full sized version can be seen here.)
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oh, the crayons vis is simply gorgeous. And, truly, what could be better than color to visualize color. Bravo.
The Good: I definitely shows how crayon colors have expanded over time. I believe you can now buy a large Crayola box with over 100 colors in it, but I may be wrong. It also gives some idea of the category all the colors all into, though there are some odd choices, like the red at the top.
The Bad: I agree with all you’ve said about the color choices for this map. I also think that if the two colors at the end of the spectrum were next to each other on the map for some reason, then I would immediately assume that one was simply a step up or down on the index from the other, not wildly different. I would note that it seems the map never has any color higher than the pink, so I wonder why they even put a legend that goes that high.