Don´t know if i´m doing anything but the accuracy in the location services are just crap on my lumia 920.
Doesn´t matter what I do. The updates are very slow and the position service are always using the cellular network to determine position.

geolocator.MovementThreshold = 1; // The units are meters.
            //geolocator.ReportInterval = 10;
            //geolocator.DesiredAccuracyInMeters = 1;
            geolocator.DesiredAccuracy = PositionAccuracy.High;
Was trying to build racing timer to determine how long it takes to drive 1/4 and 1/8 miles.
Not a chance that it will work as it takes up to 10 seconds between the updates even when I have set the movementthreshold to 0 or 1 meters.

Is there any possibility to only use the GPS in the location service?

/ Jonas