title: Device tracking without wifi or gps
body: <p>This isn't necessarily a specific code question, but more just hoping that someone might be able to point me in the right direction. I'm making an outdoors/hiking app and one of the features I'd like to build is a trail progress tracker. I've seen other apps that do this, namely maps.me, and it somehow is able to continue to track your location on a topo map even after gps and wifi are inaccessible. I've been trying to research information on how this is done but coming up with nothing, possibly because there's maybe some terminology involved that I'm not familiar with. If anyone can offer any links or hints as to what I should be looking up in relation to this, that would be fantastic.</p>
  
  <p>Thanks!</p>