Having trouble figuring out how to download maps for offline use (to avoid roaming fees). There are a number of references to GMDL but I can't find it for download to a Mac and for use in a NON unlocked iPhone. Any help please. I just want to download some city street maps for a trip I'm planning and I don't need directions. I just want to have maps I can zoom in and out of without taking a bunch of paper folding maps.