It is indeed possible to load the maps in Mappero beforehand: while internet connectivity is available, start Mappero and scroll the map to the area you want to download the maps of. Try to zoom in/out so that only the area you are actually interested in is on the screen. Then, tap on the title bar, choose "Maps" -> "Manage Maps...", go to the "Zoom" tab and click the zoom levels you are interested in. If the number of maps is on the order of tens of thousands or more, you'd better deselect some zoom levels,