Earth Scale

Hi, I'm trying to create an environment on the scale of earth, i.e. the main object is a map of earth and is 40,000,000 units wide, and I have actual scale buildings only 100 units long. It actually seems to work mostly ok but when I zoom in on the buildings, I get odd clipping effects that appear and disappear while I'm panning or orbiting around the buildings. Any ideas on how best to make this display reliably?