Welcome back, everyone, to Cartastrophe: The Blog with First-World Problems (as a reader rightly pointed out recently). Today’s effort comes to us from the folks at the Associated Press:
This choropleth appeared this morning accompanying a story I was reading online about the new population numbers out of the Census Bureau. Most of the map is unremarkable, but the legend is worth noting. According to the title on the legend, the colors indicate population growth, in thousands. But, the actual numbers in the legend are marked as percentages. It is probably unreasonable of me to believe that the population of Texas increased 20,000%, as that would put their current population somewhere above 4 billion people. I believe that these numbers are intended to be percentages, and that the title on the legend is simply incorrect. Perhaps this map was made by altering an existing product, and the author forgot to make some necessary changes.
The more subtle, and much more common, problem with the legend is the arrangement of the numbers. There’s an overlap to the data classes. If a state had 10% growth, does it go in the third class or the fourth? Better, I think, to add a decimal place to these numbers so that the separation is clear: 5.0-9.9, 10.0-14.9, etc. Gaps between classes make it plain which numbers go in which class. Alternately, a more complex solution is a redesign of the legend. It may be possible to visually clarify that the 5-10 class includes all numbers from 5 up until, but not including, 10. Here’s a mockup of something that comes to mind as a potential design solution:
That may or may not be too difficult for the average reader to interpret. It’s off the cuff, so I’m not entirely certain about its merits, but I do believe there are visual solutions to this problem as well as ones which rely on changing the numbers. The latter may be more clear, ultimately.
The colors for the choropleth are largely fine, but I think the various shades of blue are a bit too close to each other to easily match back to the legend. Reducing the classes by one, or by making the darkest blue even darker and stretching the color ramp out would help ease this.
One Nice Thing: I appreciate the author’s use of small boxes of color next to the state names in the northeast. The states get pretty small up there, and figuring out the color of Delaware can be challenging. With this solution, there are always legible swatches of color associated with each state.