Every four years, it seems, after an election the coverage of which is dominated by red/blue maps and warnings about how divided our country is, a series of news stories or blog posts will start to emerge on social media proclaiming, “no, its not a big red map with some blue islands, its a really purple map with some red and blue islands” or something like that. Actually, something like this post on Gizmodo.
But there are still problems with a purple map, and they are detailed in a post from 2014 on medium about the work of an MIT student even earlier. it is based on color theory. TL;DR: human perception of color is affected by adjacent colors. The same purple is perceived differently depending on whether there is red or blue adjacent to it.
The solution: use green to neutralize. Red and blue then desaturated toward gray to indicate the margin of victory.
There is still a problem with a map colored in this way, not that you will find any on popular news sites. That problem is population density. The map still is a geographically accurate map of the US, as most electoral maps are presented, so vast unpopulated areas are unfairly weighted in the mind of the observer. The map on Gizmodo tries to deal with that by desaturating red, blue, purple by population density, however, then we run into the color perception problem.
Enter the cartogram. A cartogram uses something that is map-like, but then skews the areas so that they reflect some other measure, like population density (2012) and 2016, or in some other cases, electoral vote density, in fact, a number of news sites did start using a variety of different cartograms to represent population, or electoral votes, include the Washington Post and FiveThirtyEight.com, and you can read more about election maps from National Geographic.
Bottom line: Don’t use a data visualization that represents area (a geographically accurate map) to represent other data like popular vote, or electoral college votes. This will skew perception, and doing so over the past decade or more has probably lead to increasing polarization in our politics.