The novel is set in the small town of Gatlin. It's the type of town wherein families have stayed there for generations. Where people are in each other's business. Where everyone knows you're secret.
I guess when you have lived all your life in a small town such as Gatlin, you would want to travel and explore the world outside of your little town and Ethan did that with the books that he reads. He put up a map on his wall and whenever, during his readings, he would encounter a place that he would want to travel to he would mark it on the map. Every so often, he would link the marks kinda like mapping out his road trip supposing that he leaves Gatlin.