This map shows population of each US county over time, from the US census. It also shows the US rail network over time, with data from Jeremy Atack at Vanderbilt. I think it's interesting to see the interdependence between them.
Source: [Hacker News](https://app.honeycombmaps.com/shared/UoeChOqwxXf3fI2PxKXRBmh_RHW-3UVa)