Currently if tracks or waypoints are loaded, but the
correct DEM is not available no error message is
generated. The user is left to figure out why the
application is simply not displaying anything useful.
It is also possible to have the application working
properly and just to add a single waypoint to a file,
that is out of the current range, and the application
again does not draw anything useful.
A pop up that says, "The route goes as far North as
42.1, while the current DEM only goes to 42N" would
help a confused user a lot.