Time for another tutorial. Recently I was trying to modify a tilemap returned from a typical public map overlay server (such as openstreetmap.org) - basically I needed a way to change black areas of the tile into transparent so that I could nicely overlay it on top of MKMapView. I searched for this for a while, found some solutions but did not really work as I wanted. Some examples used MKTileOverlayRenderer. Somehow that gave me weird results that I do not understand.