For setting some zoom level, let say we want to zoom user’s location with user location as center and 2km of area as radius. Then, we use following code

MKUserLocation *userLocation = _mapView.userLocation;
MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance (userLocation.location.coordinate, 2000, 2000);
[_mapView setRegion:region animated:NO];