Add cluster point annotations
This example demonstrates how to implement point annotation clustering using the Mapbox Maps SDK for iOS. It loads a map centered over Washington, D.C., and retrieves data about fire hydrants from a GeoJSON file. The file is decoded into a FeatureCollection containing PointAnnotations for each hydrant, which are displayed on the map. Clusters are created based on the proximity of annotations, with varying circle sizes and colors determined by the number of points within each cluster.
The custom clustering logic uses expressions to define circle radius and color based on the point count in a cluster. Additionally, the total count of hydrants in a cluster is calculated and displayed as part of the cluster annotation. Tapping on a cluster expands it, focusing the map view on the cluster's area. Customizations such as adjusting circle stroke color and width can be applied to the clusters, and the code efficiently handles the updating of layers.
iOS Examples App Available
This example code is part of the Maps SDK for iOS Examples App, a working iOS project available on Github. iOS developers are encouraged to run the examples app locally to interact with this example in an emulator and explore other features of the Maps SDK.
See our Run the Maps SDK for iOS Examples App tutorial for step-by-step instructions.
PointAnnotationClusteringExample.swift
import UIKit
import MapboxMaps
final class ViewController: UIViewController {
private var mapView: MapView!
private let clusterLayerID = "fireHydrantClusters"
private var cancelables = Set<AnyCancelable>()
override func viewDidLoad() {
super.viewDidLoad()
// Center the map over Washington, D.C.
let center = CLLocationCoordinate2D(latitude: 38.889215, longitude: -77.039354)
let cameraOptions = CameraOptions(center: center, zoom: 11)
let mapInitOptions = MapInitOptions(cameraOptions: cameraOptions, styleURI: .light)
mapView = MapView(frame: view.bounds, mapInitOptions: mapInitOptions)
mapView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
view.addSubview(mapView)
// Add the source and style layers once the map has loaded.
mapView.mapboxMap.onMapLoaded.observeNext { _ in
self.addPointAnnotations()
}.store(in: &cancelables)
}
func addPointAnnotations() {
// The image named `fire-station-11` is included in the app's Assets.xcassets bundle.
let image = UIImage(named: "fire-station-11")!
// Fire_Hydrants.geojson contains information about fire hydrants in Washington, D.C.
// It was downloaded on 6/10/21 from https://opendata.dc.gov/datasets/DCGIS::fire-hydrants/about
// Decode the GeoJSON into a feature collection on a background thread
_ = Bundle.main.url(forResource: "Fire_Hydrants", withExtension: "geojson")!
DispatchQueue.global(qos: .userInitiated).async {
guard let featureCollection = try? self.decodeGeoJSON(from: "Fire_Hydrants") else {
return
}
// Create an array of annotations for each fire hydrant
var annotations = [PointAnnotation]()
for feature in featureCollection.features {
guard let geometry = feature.geometry, case let Geometry.point(point) = geometry else {
return
}
var pointAnnotation = PointAnnotation(coordinate: point.coordinates)
pointAnnotation.image = .init(image: image, name: "fire-station-11")
pointAnnotation.tapHandler = { [id = pointAnnotation.id] _ in
print("tapped annotation: \(id)")
return true
}
annotations.append(pointAnnotation)
}
DispatchQueue.main.async {
self.createClusters(annotations: annotations)
}
}
}
func createClusters(annotations: [PointAnnotation]) {
// Use a step expressions (https://docs.mapbox.com/mapbox-gl-js/style-spec/#expressions-step)
// with three steps to implement three sizes of circles:
// * 25 when point count is less than 50
// * 30 when point count is between 50 and 100
// * 35 when point count is greater than or equal to 100
let circleRadiusExpression = Exp(.step) {
Exp(.get) {"point_count"}
25
50
30
100
35
}
// Use a similar expression to get different colors of circles:
// * yellow when point count is less than 10
// * green when point count is between 10 and 50
// * cyan when point count is between 50 and 100
// * red when point count is between 100 and 150
// * orange when point count is between 150 and 250
// * light pink when point count is greater than or equal to 250
let circleColorExpression = Exp(.step) {
Exp(.get) {"point_count"}
UIColor.yellow
10
UIColor.green
50
UIColor.cyan
100
UIColor.red
150
UIColor.orange
250
UIColor.lightPink
}
// Create expression to get the total count of hydrants in a cluster
let sumExpression = Exp {
Exp(.sum) {
Exp(.accumulated)
Exp(.get) { "sum" }
}
1
}
// Create a cluster property to add to each cluster
let clusterProperties: [String: Exp] = [
"sum": sumExpression
]
// If a feature has the point_count property then prepend "Count:" and display the sum of hydrants in the cluster
// The sum property is added here for demonstration, you can use the built-in "point_count"
// property instead: Exp(.get) {"point_count"}
let textFieldExpression = Exp(.switchCase) {
Exp(.has) { "point_count" }
Exp(.concat) {
Exp(.string) { "Count:\n" }
Exp(.get) {"sum"}
}
Exp(.string) { "" }
}
// Select the options for clustering and pass them to the PointAnnotationManager to display
let clusterOptions = ClusterOptions(circleRadius: .expression(circleRadiusExpression),
circleColor: .expression(circleColorExpression),
textColor: .constant(StyleColor(.black)),
textField: .expression(textFieldExpression),
clusterRadius: 75,
clusterProperties: clusterProperties)
let pointAnnotationManager = mapView.annotations.makePointAnnotationManager(id: clusterLayerID, clusterOptions: clusterOptions)
pointAnnotationManager.annotations = annotations
pointAnnotationManager.onClusterTap = { [weak self] context in
self?.mapView.camera.ease(to: CameraOptions(center: context.coordinate, zoom: context.expansionZoom), duration: 1)
}
// Additional properties on the text and circle layers can be modified like this below
// To modify the text layer use: "mapbox-iOS-cluster-text-layer-manager-" and SymbolLayer.self
do {
try mapView.mapboxMap.updateLayer(withId: "mapbox-iOS-cluster-circle-layer-manager-" + clusterLayerID, type: CircleLayer.self) { layer in
layer.circleStrokeColor = .constant(StyleColor(.black))
layer.circleStrokeWidth = .constant(3)
}
} catch {
print("Updating the layer failed: \(error.localizedDescription)")
}
}
// Load GeoJSON file from local bundle and decode into a `FeatureCollection`.
func decodeGeoJSON(from fileName: String) throws -> FeatureCollection? {
guard let path = Bundle.main.path(forResource: fileName, ofType: "geojson") else {
preconditionFailure("File '\(fileName)' not found.")
}
let filePath = URL(fileURLWithPath: path)
var featureCollection: FeatureCollection?
do {
let data = try Data(contentsOf: filePath)
featureCollection = try JSONDecoder().decode(FeatureCollection.self, from: data)
} catch {
print("Error parsing data: \(error)")
}
return featureCollection
}
}
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