My terrain is large - what is the world machine export process?

[anonymous_user_afd92cec]

Also - any idea what this is all about?

Sorry about this, there is a regression with tiled landscape import in 4.7. It was fixed with this change:
https://github/EpicGames/UnrealEngine/commit/56626be625707db794233559a5d2fab5cf570e8d

But it will be only in 4.8 release.