100th Meridian

 If you have taken a class with me that involves the United States in any way, you have seen me point out the 100th degree west longitude on more than one map. Often this begins when I am showing the iconic Earth at Night satellite mosaic from NASA. On that image, we can see patterns formed by the expansion of the railroad, a century after cars largely replaced rail travel. I then point out maps of political bounaries, elevation, rainfall, or whatever other maps are handy.

All of which is to say that the line has been an important part of how I think about the continent for a very long time. By now I have forgotten where I first learned of the notion -- probably one of my mentors at Miami of Ohio, where I learned to teach physical geography.