A-GPS Tracker++ allows a use of the tracker without internet, using off-line maps. The app provides also the generation of contour lines and some GPX editing functions.
MAPS: The geographic maps used by AGPS-Tracker++ are offline, free maps created and maintained by the  OpenStreetMap project (“©Openstreetmap-contributors). These maps are compressed in files with extension “.map”  and may be downloaded using A-GPS Tracker++. The first time you run the app your archive is empty and you will be invited to select the map of your country and transfer it to your local archive. You can always download other map files, of other countries, into your local folder.
CONTOUR LINES: are generated automatically by A-GPS Tracker++ when you keep pressed a point of the map. The contour lines are generated starting from Digital Elevation Map (DEM) data files. The DEMs provide an accurate altitude mapping of the terrain (one point every 30m) and have been made available by NASA. They cover all land between 56 degrees south and 60 degrees north. The first time you run the app your DEMs archive is empty. To load a DEM file you just need to keep pressed a point on the map. If you do not have a DEM for this area you will be prompted to load the file from the A-GPS Tracker++ server.
If you keep pressed a point on the map and you have already downloaded the DEM for this area, then you will see the contour lines created by A-GPS Tracker++ around the touched area.
ELEVATION: The elevation is the less precise of the data provided by GPS, it may be subject to unexpected variations. DEMs give an alternative and more stable way to calculate elevation from the knowledge of the geographical position.
GPX EDITING: A GPX track, already created in your archive, can be loaded and modified in the following ways: 
1. Merge two tracks. The first track is simply loaded, a further one may be added. 
2. Modify or Delete a Point Of Interest (POI). Select a POI to Delete it  or Modify POI name and description.
3. Add a new POI either assigned to a point on the MAP or to a point on the track. 
4. Save the resulting track to a new GPX file.