If you're using Blitz terrains, watch out because the vertices at opposite sides of a terrain are automatically adjusted so they are the same height.
That means you can put copies of the same terrain next to each other with relative ease, but putting two different terrains next to each other is going to be quite fiddly.
That means you can put copies of the same terrain next to each other with relative ease, but putting two different terrains next to each other is going to be quite fiddly.