If I start downloading map and stop it in the middle of downloading, then download the map of the same (or say locations that will overlap with whatever map I have already downloaded) then will it download all the maps again or will it share the previous data with the new download?

I was trying to download 80Km map with all possible zoom levels, I don't seem to be able to download whole map at once (left it overnight once, result was restarted device in the morning). Maybe I will use pc for downloading maps now.