Hello,Could someone explain what is a good distance or height that should be used to replace default ground textures? I understand they need to be 256x256, I just need to know how far viewed from above the earth they need to be to look to scale in the sim.Thanks in advance!

You need to experiment in Google Earth for example to see how high you must go to get 4.75 meters/pixel for FS9. Presumably you want to make many ground textures as well..just one wouldn't look very good. The lower your altitude, the more stitching together you will have to do, but the better your quality will be.