I used this picture (https://i.gyazo.com/11cf7f9b1d33e81e03fb5c373618266d.jpg) as the background, as I wanted it to have a Native American feel to it. I could have made it more detailed if I wanted, but I wanted the focus to be on the map itself, not the background.
As for the Cimarron/Harmon connection, I definitely considered that. However, I, personally, prefer it the way it is; just Oklahoma. No shortcuts through Texas. If enough people request it, though, I'll add it. Thanks for the feedback!