Drawing a poly line on a mapview in Swift 3

mapViewPolyLine.swift

func somewhereElse() {
  let startLocation  = CLLocation(latitude: startLat, longitude: startLon)
  let endLocation = CLLocation(latitude: endLat, longitude: endLon)
  let locations = [startLocation,endLocation]
  var coordinates = locations.map({(location: CLLocation!) -> CLLocationCoordinate2D in return location.coordinate})
  let polyline = MKPolyline(coordinates: &coordinates, count: locations.count)
        mapView.add(polyline)
}
    
    func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
        if overlay.isKind(of: MKPolyline.self) {
            // draw the track
            let polyLine = overlay
            let polyLineRenderer = MKPolylineRenderer(overlay: polyLine)
            polyLineRenderer.strokeColor = UIColor.blue
            polyLineRenderer.lineWidth = 2.0
            
            return polyLineRenderer
        }
        
        return MKPolylineRenderer()
    }