I don't have mapsource. I have BaseCamp. BaseCamp works with mapinstall that I have. With the unit pluged in, (forget about mapinstall for just a second) does anybody know how to select a section of a map in basecamp and transfer. I know that when I hit transfer it goes to mapinstall and it sees my garmin unit because its pluged in. I just want to find out how to use basecamp without transfering the whole thing.