Doubts on Summoner's Rift Mesh

Hello there! I've always wanted to make a map similar to SR, but I have a few doubts as to how SR was made. Is it like one huge mesh? Or are they divided into quadrants? Or are the props in the map separate meshes? Having separate meshes sound easy, especially for texturing, but I assume there'd be way too many lightmaps! But having bigger meshes mean the texturing would require HUUGE texture files.

I'm confused as to how to approach this. I'd really appreciate it if any of the Rioters could shed some light on how the 3d production for SR was done? o.o Many thanks!