GeoCoordinateWatcher watcher = new GeoCoordinateWatcher();
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
var myPosition = watcher.Position;
longTxtBlock.Text = (myPosition.Location.Longitude).ToString();
latiTxtBlock.Text = (myPosition.Location.Latitude).ToString();
base.OnNavigatedTo(e);
}