Drowning in colors

This tile map I saw on a news site left me perplexed. The headline tells me it's about the upcoming midterm elections in the U.S. Senate: how the Democrats feel more confident about their chance of gaining control of it.Up top, it mentions 35 seats are up for grabs. That is the extent of the legend. (My brain kept mistaking the two squares on the bottom left as part of the legend, but this version of the tile map pairs up Alaska and Hawaii, depositing them there.) I happened to be meeting with a politically active friend at the time, and she was able to figure the chart out without much trouble. So the problem lies with me, or anyone who's not already steeped in the world of elections.The designer relies on the reader to bring a lot of knowledge. That each state has exactly two senators, which is why each square is divided into two triangles. If the triangle has an outline, that seat is being contested. In the diagram above, states fall into two groups: those with no elections this…