Every time Twilight looks at an atlas, or a map, she sees something that bothers her. After being unable to find the answer with research, she chooses instead to go to one of the two ponies who is bound to have the answer; Princess Celestia herself.

Just why does every place have a pony pun for a name?

No idea who the source of the cover image is, if someone lets me know I will be happy to credit them.