All the location info (pins, notes, etc) are stored locally. Offline functionality isn't explicitly supported for the map itself but the default behaviour of the system is to cache quite a lot of map-tile information. As long as before you go offline you "inspect" the areas of the map you want to use you should be fine. I've used it offline a few times myself and it works reasonably well. I'd say the feasibility depends on whether you're walking around a city (small map areas) vs going on a road trip (huge map areas). Hope that helps!