Related to http://stackoverflow.com/q/41430255/1271826

CustomAnnotationViewHitTest.swift

class CustomAnnotation: MKPointAnnotation {
    var color = UIColor.red
    var size = CGSize(width: 20, height: 20)
}

class ViewController: UIViewController {

    @IBOutlet weak var mapView: MKMapView!
    
    @IBAction func didTapButton(_ sender: UIButton) {
        let annotation = CustomAnnotation()
        annotation.coordinate = mapView.centerCoordinate
        switch arc4random_uniform(14) {
        case 0: annotation.color = .black
        case 1: annotation.color = .blue
        case 2: annotation.color = .brown
        case 3: annotation.color = .cyan
        case 4: annotation.color = .darkGray
        case 5: annotation.color = .gray
        case 6: annotation.color = .green
        case 7: annotation.color = .lightGray
        case 8: annotation.color = .magenta
        case 9: annotation.color = .orange
        case 10: annotation.color = .purple
        case 11: annotation.color = .red
        case 12: annotation.color = .white
        case 13: annotation.color = .yellow
        default: annotation.color = .black
        }
        let side = Int(arc4random_uniform(80) + 40)
        annotation.size = CGSize(width: side, height: side)
        mapView.addAnnotation(annotation)
    }

}

extension ViewController: MKMapViewDelegate {
    func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
        if annotation is MKUserLocation { return nil }
        guard let customAnnotation = annotation as? CustomAnnotation else { fatalError("should have been CustomAnnotation") }
        
        let identifier = "myid"
        var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: identifier)
        if annotationView == nil {
            annotationView = MKAnnotationView(annotation: annotation, reuseIdentifier: identifier)
        } else {
            annotationView?.annotation = annotation
        }
        annotationView?.image = customImage(customAnnotation.color, size: customAnnotation.size)
        
        return annotationView
    }
    
    func mapView(_ mapView: MKMapView, didSelect view: MKAnnotationView) {
        print("didSelect")
        DispatchQueue.main.async {
            mapView.deselectAnnotation(view.annotation, animated: false)
        }
    }
    
    func customImage(_ color: UIColor, size: CGSize, scale: CGFloat = 0) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(size, false, scale)
        color.setFill()
        UIBezierPath(ovalIn: CGRect(origin: .zero, size: size)).fill()
        let image = UIGraphicsGetImageFromCurrentImageContext()!
        UIGraphicsEndImageContext()
        return image
    }
}