Question

Say I have a square which consists of four CLLocationCoordinate2D points, which are in lat, lon, and I want to find the area of the square in meters. I convert the CLLocationCoordinate2D points into MKMapPoints, and I find the area in X-Y space. However, the area I find is in the units of MKMapPoint, which don’t directly translate to meters. How can I translate this area in MKMapPoint-space back into meters?

Answer 1

The MapKit function MKMetersBetweenMapPoints makes this easier.

For example, if you wanted to get the area of the currently displayed region:

MKMapPoint mpTopLeft = mapView.visibleMapRect.origin;

MKMapPoint mpTopRight = MKMapPointMake(
    mapView.visibleMapRect.origin.x + mapView.visibleMapRect.size.width, 
    mapView.visibleMapRect.origin.y);

MKMapPoint mpBottomRight = MKMapPointMake(
    mapView.visibleMapRect.origin.x + mapView.visibleMapRect.size.width, 
    mapView.visibleMapRect.origin.y + mapView.visibleMapRect.size.height);

CLLocationDistance hDist = MKMetersBetweenMapPoints(mpTopLeft, mpTopRight);
CLLocationDistance vDist = MKMetersBetweenMapPoints(mpTopRight, mpBottomRight);

double vmrArea = hDist * vDist;

The documentation states that the function takes “into account the curvature of the Earth.”