I've been playing around with GPS mapping software in preparation for a backpacking trip I'm taking. So far I've settled on using Maemo Mapper because it has the ability to download the topographical maps. Of course, while downloading the maps I've found myself caught with deciding how much detail versus how much coverage I want.

To that end, I was wondering how exactly does Maemo mapper store the downloaded tiles. Are they stored as gifs, jpegs, some other format? Would it be possible for setting a compression level to the tiles as they are downloaded and saved? I understand there would be a loss in the quality of the tiles by doing this but if it saves me some space I could download the lower quality tiles for areas I "might" need in the future if I happened to travel to that part of a state or something.

jpegs and pngs, which means they're already compressed. The tiles exist, as far as I know, in only one version (that is, only one compression level available), but someone please correct me if that's not true.
In any case I don't think it would pay to decompress and recompress to some other compression level during download, it's barely fast enough as it is..