title: MapKit pin title not visible when placed on overlay?
body: <p>When I place a pin on top of an overlay, the title of the pin appears to be obscured. When the pin is placed over a point that is not on top of the overlay, the title appears below the pin.</p>
  
  <p>The string lastCoordName is the title of the pin; this string is passed from the previous view controller to the current one (shown below). </p>
  
  <p>Here are some images to describe what I'm talking about...</p>
  
  <p><a href="https://i.stack.imgur.com/UN7eQ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/UN7eQ.jpg" alt="title shown"></a>
  Above image shows the title right below the pin ("360") when the pin is off the overlay. </p>
  
  <p><a href="https://i.stack.imgur.com/bVdha.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bVdha.jpg" alt="title not shown"></a>
  But the title goes away when the pin is moved to the correct position on top of the overlay. </p>
  
  <p>The title is still shown when the polyline is drawn horizontally and terminates off the overlay, so the problem isn't that the line is covering the title. </p>
  
  <p>Here is the custom pin class:</p>
  
  <pre><code>class CustomPin : NSObject, MKAnnotation {
      var coordinate: CLLocationCoordinate2D
      var title: String?
  
      init(coordinate: CLLocationCoordinate2D, title: String) {
          self.coordinate = coordinate
          self.title = title
  
          super.init()
      }
  }
  </code></pre>
  
  <p>The relevant part of viewDidLoad()</p>
  
  <pre><code>    let pin = CustomPin(coordinate: endPoint, title: lastCoordName)//uses lastCoordName from previous vc (insead of looking up name of last node given coord)
      mapView.addAnnotation(pin)
      mapView.selectAnnotation(pin, animated: true)
  </code></pre>
  
  <p>And the mapViewController extension</p>
  
  <pre><code>extension mapViewController: MKMapViewDelegate {
  
      func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -&gt; MKOverlayRenderer {
          if overlay is SchoolMapOverlay {
              return SchoolMapOverlayView(overlay: overlay, overlayImage: #imageLiteral(resourceName: "GBSF1"))
          } else if overlay is MKPolyline {
              let lineView = MKPolylineRenderer(overlay: overlay)
              lineView.strokeColor = UIColor(red:0.2, green:0.48, blue:1.00, alpha:1.0)
              lineView.lineWidth = 10.0
              return lineView
          }
          return MKOverlayRenderer()
      }
  
      func mapView(mapView: MKMapView, viewForAnnotation annotation: MKAnnotation) -&gt; MKAnnotationView? {
          let pin = MKPinAnnotationView(annotation: annotation, reuseIdentifier: "pin")
          pin.canShowCallout = true
  
          return pin
      }
  }
  </code></pre>
  
  <p>Is the overlay covering the pin title? If so, why are the pin and its title not on the same level (above the overlay)? </p>