как использовать GPS на карте Google в Objective-C

в viewDidLoad написать

self.locationManager = [[[CLLocationManager alloc] init] autorelease];
self.locationManager.delegate = self; // Tells the location manager to send updates to this object

self.mapView.delegate = self;
self.locationManager.desiredAccuracy = kCLLocationAccuracyBest;
[self.locationManager startUpdatingLocation];

а затем реализовать

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation

метод делегата newLocation будет местоположением пользователя

locationManager — это CLLocationManager * locationManager;