I'm a relatively new Garmin user (I have the 276C) and I have a question about downloading mapsets from my PC to my GPS. Several weeks ago I highlighted a series of maps and downloaded them to the GPS in anticipation of riding to the MOA rally in Lima, Ohio. In checking the detailed maps on the GPS I see that I should have downloaded more detailed maps around the rally site. My question: can I simply select a few more detailed maps in Mapsource on my PC and download them to my GPS (thereby adding them to the maps already in the GPS) or do I have to create an entirely new mapset to download (because I'd effectively be "erasing the maps already in my GPS by downloading a few new ones)? I think I know the answer, but I'd like to be sure before wasting time. Thanks.