What is Just Beyond Fallout 4's Borders?

What lies beyond the borders in Fallout 4 and what could have been there? Mr. House has tasked nvRanger & Co. with mapping it out. More videos of this sort: https://www.youtube.com/watch?v=1YLYjFzJdyQ&list=PLNqbI_-fOWnhjjTR_TDdjBnNMY1lsd69_