Drecknich

I'm working on a little expansion to the Long 15 and I was wondering if there is any reason I shouldn't use the already generated and unused terrain past the Mojave Outpost fence? I've noticed that the terrain on the very edge of the map starts to flicker if you get close and that gives me pause to start building. I've read through what little documentation I can find on the subject of GECK terrain but I can't find anything that references that specific issue. I'm assuming it's a long distance flag I've missed somewhere and if so, how would I go about removing it. I'm totally new to terrain manipulation so excuse my ignorance. Any help would be greatly appreciated. Thanks!