Also if ever you try extending the size of your map. As long as two planes touch it's possible to walk across them. It is hard to make them seamlessly blend into one another even if the coordinates are exact though. That's more into learning map design. If you do end up using multiple terrains you're going to need an AI seeder per piece of terrain. This also applies to enclosed building instances without any doors. The walls will block them off and turn everything red.
