I have world composition enabled. I have 4 maps that are “attached” in the world composition editor. However, when I edit the height of one of the landscapes where it meets another landscape, it doesn’t sticth the two together.
So any height difference between the two ends up creating holes in my landscape. Any ideas?
The easiest solution is to create the landscape as one single part + after you have made all changes, split it up and import everything.
Otherwise you will have to fix it manually -> in this thread you can find more information about that: https://forums.unrealengine/showthread.php?70769-Edit-Multiple-Landscapes 
Much appreciated.
For the sake of completeness. In order to sculpt across landscape borders you have to import from .raw files and import as a tiled landscape.
Otherwise UE4 won’t stitch across sublevels.
You have to “use” it as one single landscape -> then you can split it up into parts + use it for the world composition tool
It is possible to add to landscape while making. So start off how ever and it doesnt have to be square. There is a area in landscape that alolows you to add to exsiting but u cant conect differents ones I will go and look to see where this is
try this. Just looked at it. best thing ever for time saving. https://forums.unrealengine/showthread.php?68886-Here-is-a-tutorial-for-L3DT-and-UE4