WIRED has a nice explainer of various electoral map cartograms.
EVERY MAP MAKES COMPROMISES. The Mercator projection, which sacrifices accurate geography for nice, straight lines, is a classic example. Electoral cartograms, which visualize the political climates of individual states, are another.
“They’re all working off the same data, but there’s lots of room to make choices and prioritize information,” says Noah Veltman, a data visualization expert on WNYC’s data news team. So the same data can end up looking pretty different—as in this morphing animation, which Veltman created. It compares cartograms from FiveThirtyEight, the Washington Post, the Wall Street Journal, NPR andDaily Kos, to illustrate how different designers go about presenting electoral data.