True North depends on GPS for location

[hackerb9]

I just noticed that when I try to use Compass indoors it shows a "Waiting for Location Update" warning with a spinning circle. This happened because I had enabled "True North", which depends on GPS.

Falling back to magnetic North was fine, but it would have been better if Compass let me use the last known location.

Ideally, I'd be able to change the magnetic correction manually in Settings by specifying an angle. Optionally, it would be nice to set the offset by simply tapping on a map of the world.