There are a lot of ways to understand the history of American politics over the past century.
It's all here:
* The South as the backbone of the Democratic House majority from the 1950s until it became the backbone of the Republican majority in the mid 1990s.
* The hollowing-out of the Republican party in the Northeast over the past decade or so.
* The Midwest's movement from solidly Republican to swing-y, a process that began, in earnest, in the 1960 election.
* The clumping of like communities in recent years, as more and more advanced technology allowed for more precise splitting of congressional lines during the redistricting process.
You can pause the map above, speed it up or reverse it. You can also shrink the time period it displays. It's pretty amazing -- and a pretty amazing time suck.
(Thanks to Pew's Drew DeSilver for flagging it for us.)