Convert pixel length to latitude longitude difference iOS

//  1.  Get difference from center of map to top middle of map (200 pixel difference).

//  2.  Convert this pixel difference into difference of latitude

//  3.  Reset the mapView center point with the new offset

//Grab the pixel difference from the center of the mapview

CGPoint centerOfMap = CGPointMake(mapView.frame.size.width/2, mapView.frame.size.height/2);

CGPoint topMidOfMap = CGPointMake(centerOfMap.x, centerOfMap.y-200); //Step 1

//Now get difference of longitude and latitude

CLLocationCoordinate2D centerOfMapCoord = [mapView convertPoint:centerOfMap toCoordinateFromView:mapView];   //Step 2

CLLocationCoordinate2D topMidOfMapCoord = [mapView convertPoint:topMidOfMap toCoordinateFromView:mapView]; //Step 2

CGFloat latitudeDiff = topMidOfMapCoord.latitude - centerOfMapCoord.latitude; //Step 2

coord.latitude -= latitudeDiff;

[mapView setCenterCoordinate:coord zoomLevel:default_zoom animated:NO]; //Step 3