Getting user's location in iOS is different from MKMapView and CLLocationManager

Question

Im using CLLocationManager to get the location of the user, otherwise Im using MKMapview to display on the map.

 - (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations 
{
   16.50374457,+80.66301357 // lat and long 
}


-(void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation
{

 CLLocationCoordinate2D loc = [userLocation coordinate];

//(latitude = 16.507553768993734, longitude = 80.664011964856343)
}

The two results were slightly different. According to my observation, the second is the most accurate. AS R and D MKMapview uses the internal Cllocation manager, but why am I getting the differences?