Hello.
I have 510 terrains with these specifications (written below) and my Unity game engine is the latest version of 5.3.6.
When I want to start light mapping them in an empty scene, it crashes and is unsuccessful. 
Please help, what on the earth should I do.
Thanks in advance.
Reading some articles in reddit and CryEngine forums, I found people who wanted to make huge scenes are mad at Unity3D. I don’t know, but all I want is to how to apply lightmap to my huge scene. There should be a way for it.
I’m no expert about terrains but what I read is that you should set the baking resolution really really low for terrains. Like 0.1 or 0.01.
I’ve used 0.0128 and still keeps crashing, thanks for the reply though.
Is it possible to bake them in other scenes individually and merge them into the main scene?.
I think so. You can copy and paste assets from one scene to another… Try baking a single terrain in its own scene then move it into your main scene.
Just a simple question. You are currently using the Unity’s terrain, but could you use some big meshes instead of terrain? Would it completely be undoable? (Personnaly I never use the terrains, they are too much troubles)
Also, when you try to bake them, do you bake them one by one? (You could bake each one of them in a different scene, then put them all together using additive scene load.
On last trick that I used to speed up dynamic GI baking (don’t know if it works for lightmapping) is to put my whole scene temporarily on an empty mesh, an scale it down for the baking. Then when you scale it back to the original size, the lighting is still present.
Hope it helps, and good luck! 
Thanks for the reply, I can’t use meshes instead of Terrain. Well I don’t think making 500+ scenes and loading them is a good idea.