To have two or more items import in relational positions, I believe they need to have been created (or exported) in those positions to begin with. In other words, if the DEMs you brought in weren't in next-to-each-other positions when they were created/exported, they'll import as individual objects instead of related objects. Hope that makes some sense okay. I'm not a DEM expert. (Where is Cheers when you need him?) I've used some rather large image maps up to 5000 x 5000. No problem, and I would suspect that they could be larger. It takes a little while for the material to load when you first apply it (or when you open a scene containing it), but there's no noticeable slowness after that initial bit. :)