Reuse area definition for different maps
Sometimes you are interested in more than one map type for the same area. It would be useful to be able to reuse the area definition of a downloaded map to download another type.
Example: I want to go to Mt. Ranier, WA (USA). I discover that the Google maps has very useful info about towns, roads, etc,, but very poor info for the backcountry. At the same time, USA Topo is ok for the backcountry, but outdated and difficult to read for the rest. It would be nice to be able to define the interesting area just once, and then download both the Google maps and the USA Topo tiles.
The easiest (for the user) and most flexible way of doing this, in my opinion, is to just add an option "use existing map" in the "download map" dialog window. If the user choose that option, a list of the already downloaded maps is presented, so that the user can pick one and have the downloaded area defined by whatever is covered by that map.