title: Updating MKMapView to CLPlacemark returned from CLGeocoder
body: <p>I want to be able to update the region displayed on a MKMapView by allowing the user to type in an address or location in a UIAlertView. I currently have:</p>
  
  <pre><code>        if (geocoder.geocoding)
              [geocoder cancelGeocode];
  
          [geocoder geocodeAddressString:[[alertView textFieldAtIndex:0] text] completionHandler:^(NSArray *placemarks, NSError *error) {
              if (!error) {
                  NSLog(@"Found a location");
              } else {
                  NSLog(@"Error in geocoding");
              }
  
              NSLog(@"Num found: %d", [placemarks count]);
  
              CLPlacemark *placemark = [placemarks objectAtIndex:0];
              MKCoordinateRegion region;
              region.center.latitude = placemark.region.center.latitude;
              region.center.longitude = placemark.region.center.longitude;
              MKCoordinateSpan span;
              double radius = placemark.region.radius / 1000;
  
              NSLog(@"Radius is %f", radius);
              span.latitudeDelta = radius / 112.0;
              //span.longitudeDelta = ??? 
  
              region.span = span;
  
              NSLog(@"Region is %f %f %f", region.center.latitude, region.center.longitude, span.latitudeDelta);
  
              [mapView setRegion:region animated:YES];
          }];
  </code></pre>
  
  <p>My problem is I am unsure how to calculate the longitude delta. </p>