MapView unable to convert Lat/Long to Double

I am trying to set the mapView based on Lat Long but I belive they need to be set as Double and not String?!

if let articlesFromJson = json["articles"] as? [[String:AnyObject]] {
                    for articleFromJSON in articlesFromJson{
                        if let title = articleFromJSON["CompanyName"] as? String, let desc = articleFromJSON["SICDescriptions"] as? String, let latitude = articleFromJSON["lat"] as? String, let longitude = articleFromJSON["lon"] as? String {
                           
                            DispatchQueue.main.async {
                                self.mainTitle.text = title
                                self.subMainTitle.text = desc
                                let lat:CLLocationDegrees = latitude
                                let lon:CLLocationDegrees = longitude
                                let deltaLatitude: CLLocationDegrees = 0.01
                                let deltaLongitude: CLLocationDegrees = 0.01
                                let span: MKCoordinateSpan = MKCoordinateSpanMake(deltaLatitude, deltaLongitude)
                                let location: CLLocationCoordinate2D = CLLocationCoordinate2DMake(lat, lon)
                                let region: MKCoordinateRegion = MKCoordinateRegionMake(location, span)
                                self.mapView.setRegion(region, animated: true)
                            }
                        }
                       
                    }