You could use MapKit for that:
- (CLLocationCoordinate2D *) calculateSquareCoordinates:(CLLocation*)center withRadius:(float)radius{
MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance(center.coordinate, radius*2, radius*2);
CLLocationCoordinate2D points[4];
points[0] = CLLocationCoordinate2DMake(region.center.latitude - region.span.latitudeDelta/2, region.center.longitude - region.span.longitudeDelta/2);
points[1] = CLLocationCoordinate2DMake(region.center.latitude + region.span.latitudeDelta/2, region.center.longitude - region.span.longitudeDelta/2);
points[2] = CLLocationCoordinate2DMake(region.center.latitude + region.span.latitudeDelta/2, region.center.longitude + region.span.longitudeDelta/2);
points[3] = CLLocationCoordinate2DMake(region.center.latitude - region.span.latitudeDelta/2, region.center.longitude + region.span.longitudeDelta/2);
return points;
}
and just call
CLLocationCoordinate2D *fourPoints = [self calculateSquareCoordinates:center withRadius:1000];
on your code.