I created a large landscape and when i try to build the lighting on Preview, it runs out of memory.
I have a lightmass importance volume around the bounds of the level.
Now obviously this is a large swathe of terrain to light, but apparently we can tile tons of these large landscapes together so this is not overly large compared to what some will be doing with it. What am I doing wrong?
It is indeed possible to make larger worlds than an 8k landscape, but you’ll be using smaller, tiled landscapes and build their light separately. So it is quite normal for an 8K landscape to require a lot of ram. One way to get around it is to increase the virtual memory in your OS, and the other one is to get more RAM.
Yeah, I have 16GB RAM and a 2GB pagefile.
I know that’s not a lot these days in terms of RAM but I’m surprised that on Preview settings for a standard (Admittedly large) size landscape, it would run out of RAM.
Well, I’m having no luck whatsoever trying to tile the landscape from smaller parts either so overall I’m not very happy at the moment with my progress. There’s always something that doesn’t work and despite the amount of tutorials out there, they never quite cover everything 
I’ll keep experimenting, cheers
Increase pagefile to 8 if you can, and also look at World Composition if you havent already.
Edit: I would also consider dynamic lighting(LPV if you want dynamic GI) if you are making an open world game.
This thread details the changes needed for changing to dynamic lighting:
