Boy, you can sure tell where the east-west division in the USA with this map of D1 schools. Basically the line is I-35 in Texas and Oklahoma; US 81 in Kansas and Nebraska; and then I-29 in South and North Dakota.
There are so many different charts that create that perfect divide in the United States. It pretty cool to see how D1 schools create another vertical line on the 98th meridian. Like the graft above shows, it all starts and ends with rain fall. Not only for keeping humans/animals alive but it creates tree biodiversity which leads to more/different bugs, which brings in the birds/small critters that get ate up by bigger mammals, and ultimately leads to our dinner plate. It's also interesting how small towns aren't nearly as abundant as they are in the eastern side of the US. The West essentially has to live in cities to be able to tap into natural resources (Las Vegas, Salt Lake City, Bozeman, etc.). You won't meet too many people from a small town in Wyoming, New Mexico, Utah.