Hi we are planning to make a truck delivery game but with a huge city level more or less similar or atleast smaller than GTA, but it will be a city and sometimes deliver across city. How to go with this? As I know modelling a huge 3D level and loaded it all together eats up RAM and GPU memory as well as slow (rendering multiple polygon). Does Unity implements some sort of Octree/Quadtree or optimization explicitly or something, or how should it work? like say for example in GTA (I know they are using their own engine), where you can go on top a certain mountain and can still see the buildings from a far though with less poly (thru mipmaps or LOD) but still am wondering how to go about this in Unity. Any advice?