gistfile1.txt

 private func loadPins() {
        var lamps = viewModel.batchLamps(forRect: mapView.visibleMapRect)

        if lamps.count == 0 {
            mapView.removeAnnotations(mapView.annotations)
            return
        } else if lamps.count > 100 {
            let range = 100...lamps.count - 1
            lamps.removeSubrange(range)
        }

        //Get non-visible existing annotations:
        let nonVisible = mapView.annotations.filter { (annotation: MKAnnotation) -> Bool in
            return lamps.contains(where: { $0.id != annotation.title })
        }
        mapView.removeAnnotations(nonVisible)

        let unique = lamps.filter { (lamp: Lamp) -> Bool in
            return !mapView.annotations.contains(where: { $0.title == lamp.id })
        }

        let annotations = unique.map({ return convertLamp($0) })
        mapView.addAnnotations(annotations)
    }