The railroad track runs off the edge either because that’s just how the designer created it, or maybe because you could conceivably add wooden track and extend the playing area off the mat. But, the point of the playscape is to play on the playscape, right?

However, you bring up a great idea. After I photographed the mats, my daughter had all four sprawled on the floor. It would be spectacular if the edges fit together like a puzzle, but that might not jive with, say, combining a farm scene with a dinosaur landscape.