let topLeft: CLLocationCoordinate2D = mapView.projection.visibleRegion().farLeft
let bottomLeft: CLLocationCoordinate2D = mapView.projection.visibleRegion().nearLeft
let lat = Double(fabs(Float(topLeft.latitude - bottomLeft.latitude)))
let metersPerPixel: Double = Double((cos(lat * .pi / 180) * 2 * .pi) * 6378137 / Double((256 * pow(2, zoom))))