Okay, I'm not getting as into this as you guys are, some of this stuff is way beyond me! Interesting read, though. I'll keep an eye on this or other threads to see what you guys come up with. I have a quick question, though. After reading some of this stuff, I went and DL'd a couple of 10 m DEM's from GIS data depot. When I unzipped the archive, the only files in there were .ddf files, which no program that I have can open (Vue or 3Dem). I thought these were supposed to be SDTS files. Help?