I am having having problems editing a very large map?

I’m doing a little (more like big) experiment with a terrain set at 50000w x 50000L x2000H, but when ever i scroll in close to the terrain to modify areas that need wore detail the scene camera clips threw the terrain. this makes it almost impossible to place single trees, props,lights, or edit the terrain with roads or streams. is there any way to get past this?

go to the terrain menu under the set resolution and lower it. I usually just work on a series of 250 x 250 terrain tiles and call them as needed.