如何在iOS中使用多个注解来增加Apple Mapkit的缩放

import MapKit
import CoreLocation

class MyAnnotation: NSObject, MKAnnotation {
    var coordinate: CLLocationCoordinate2D
    var title: String?
    var subtitle: String?
    
    init(coordinate: CLLocationCoordinate2D, title: String?, subtitle: String?) {
        self.coordinate = coordinate
        self.title = title
        self.subtitle = subtitle
    }
}

let mapView = MKMapView(frame: CGRect(x: 0, y: 0, width: view.frame.width, height: view.frame.height))
mapView.delegate = self
view.addSubview(mapView)

let annotation1 = MyAnnotation(coordinate: CLLocationCoordinate2D(latitude: 40.7128, longitude: -74.0060), title: "New York", subtitle: "The Big Apple")
let annotation2 = MyAnnotation(coordinate: CLLocationCoordinate2D(latitude: 34.0522, longitude: -118.2437), title: "Los Angeles", subtitle: "City of Angels")

mapView.addAnnotations([annotation1, annotation2])

extension ViewController: MKMapViewDelegate {
    func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
        guard annotation is MyAnnotation else {
            return nil
        }
        
        let identifier = "annotationIdentifier"
        var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: identifier)
        
        if annotationView == nil {
            annotationView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: identifier)
            annotationView?.canShowCallout = true
        } else {
            annotationView?.annotation = annotation
        }
        
        return annotationView
    }
}