Convert span value into meters on a mapview

Question

Whenever the user zoom in or out the map i need to know how many meters are currently represented on the map (width or height).

What i need is the inverse function o

Answer 1

- (void)mapView:(MKMapView *)map regionDidChangeAnimated:(BOOL)animated {
  MKCoordinateSpan span = mapView.region.span;
  NSLog(@" 1 = ~111 km -> %f = ~ %f km ",span.latitudeDelta,span.latitudeDelta*111);
}

According to the docs http://developer.apple.com/library/ios/#documentation/MapKit/Reference/MapKitDataTypesReference/Reference/reference.html,

latitudeDelta

The amount of north-to-south distance (measured in degrees) to display on the map. Unlike longitudinal distances, which vary based on the latitude, one degree of latitude is always approximately 111 kilometers (69 miles).