override func viewDidLoad() {
        super.viewDidLoad()

        contentView = ClusteringView()
        view = contentView

        let builder = ClusterBuilder()
        builder?.image = UIImage(named: "marker_black.png")
        builder?.elements = [Int: NTMarkerStyle]()

        contentView.initializeClusterLayer(builder: builder!)

        DispatchQueue.global().async {

            let path = Bundle.main.path(forResource: "cities15000", ofType: "geojson")

            guard let json = try? NSString(contentsOfFile: path!, encoding: String.Encoding.utf8.rawValue) else {
                return
            }

            // Create a basic style, as the ClusterElementBuilder will set the real style
            let builder = NTMarkerStyleBuilder()
            builder?.setColor(Colors.green.toNTColor())
            builder?.setBitmap(builder?.getBitmap())

            let style = builder?.buildStyle()

            // Read GeoJSON, parse it using SDK GeoJSON parser
            let reader = NTGeoJSONGeometryReader()
            reader?.setTargetProjection(self.contentView.map.getOptions().getBaseProjection())

            let features = reader?.readFeatureCollection(json as String!)

            let elements = NTVectorElementVector()
            let total = Int((features?.getFeatureCount())!)


            for i in stride(from: 0, to: total, by: 1) {
                // This data set features point geometry, however, it can also be LineGeometry or PolygonGeometry
                let geometry = features?.getFeature(Int32(i)).getGeometry() as? NTPointGeometry
                elements?.add(NTMarker(geometry: geometry, style: style))
            }

            DispatchQueue.main.async(execute: {
                self.contentView.addClusters(elements: elements!)
            })
        }

    }