iOS MKMapView Setting Zoom level

It was surprising initially that MKMapView doesn't really have a built in method to set the zoom level of the map. Having all the time spent using the Google Map Services MapView, this was little embarrassing. However, searching around a bit, revealed some good solutions, which it looked to be good one is in the link in the references.

The concept works by spanning the map. Below is the overall idea of spanning.

 // convert center coordiate to pixel space

    double centerPixelX = [self longitudeToPixelSpaceX:centerCoordinate.longitude];

    double centerPixelY = [self latitudeToPixelSpaceY:centerCoordinate.latitude];

    

    // determine the scale value from the zoom level

    NSInteger zoomExponent = 20 - zoomLevel;

    double zoomScale = pow(2, zoomExponent);

    

    // scale the map’s size in pixel space

    CGSize mapSizeInPixels = mapView.bounds.size;

    double scaledMapWidth = mapSizeInPixels.width * zoomScale;

    double scaledMapHeight = mapSizeInPixels.height * zoomScale;

    

    // figure out the position of the top-left pixel

    double topLeftPixelX = centerPixelX - (scaledMapWidth / 2);

    double topLeftPixelY = centerPixelY - (scaledMapHeight / 2);

    

    // find delta between left and right longitudes

    CLLocationDegrees minLng = [self pixelSpaceXToLongitude:topLeftPixelX];

    CLLocationDegrees maxLng = [self pixelSpaceXToLongitude:topLeftPixelX + scaledMapWidth];

    CLLocationDegrees longitudeDelta = maxLng - minLng;

    

    // find delta between top and bottom latitudes

    CLLocationDegrees minLat = [self pixelSpaceYToLatitude:topLeftPixelY];

    CLLocationDegrees maxLat = [self pixelSpaceYToLatitude:topLeftPixelY + scaledMapHeight];

    CLLocationDegrees latitudeDelta = -1 * (maxLat - minLat);

    

    // create and return the lat/lng span

    MKCoordinateSpan span = MKCoordinateSpanMake(latitudeDelta, longitudeDelta);

References:
http://troybrant.net/blog/2010/01/set-the-zoom-level-of-an-mkmapview/