MKMapView's user location is wrong on startup or resume

Question

When I start my application fresh, or resume after a long time, MKMapView\'s notion of the userLocation is wrong and shows me in the middle of the sea.

I am using th

Answer 1

When using CLLocationManager directly, you normally get a cached location in the first callback. It's normally a good location, although old. After that you quickly get additional callbacks giving better locations using wifi, cell tower (if available). If you have asked for < 1000m accuracy you will (after more seconds) get GPS triangulation.

None of those should be inaccurate enough to be in the middle of the ocean. I suspect that the this line of code:

self.mapView.centerCoordinate = self.mapView.userLocation.location.coordinate;

is accessing the coordinate while userLocation or location is nil. If userLocation or location is nil, this will return 0 coordinates. The location of lat=0, lon=0 is in the Atlantic Ocean, off the coast of Africa. You could add a check of location to make sure it is not nil before getting the coordinate from it, ie:

if (self.mapView.userLocation.location) {
    self.mapView.centerCoordinate = self.mapView.userLocation.location.coordinate;
    [mapView setCenterCoordinate:self.mapView.userLocation.location.coordinate zoomLevel:ZOOM_LEVEL animated:YES];           
}

You will also want to wait for callbacks to the MKMapViewDelegate mapView:didUpdateUserLocation: to know when there is a valid location available. Your implementation of didUpdateUserLocation: should discard any location that has a horizontalAccuracy < 0 which indicates an invalid location.

-(void)mapView:(MKMapView*)mapView didUpdateUserLocation:(MKUserLocation*)userLocation
{
    if (userLocation.location.horizontalAccuracy > 0) {
        [mapView setCenterCoordinate:self.mapView.userLocation.location.coordinate zoomLevel:ZOOM_LEVEL animated:YES];           
    }
}