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SwiftUI - Clustering data

Display GeoJSON data with clustering using custom layers and handle interactions with them.

ClusteringExample.swift
import SwiftUI
@_spi(Experimental) import MapboxMaps
private enum Id {
static let clusterCircle = "clustered-circle-layer"
static let point = "unclustered-point-layer"
static let count = "cluster-count-layer"
static let source = "fire-hydrant-source"
}
@available(iOS 14.0, *)
struct ClusteringExample : View {
struct Detail: Identifiable {
var id = UUID()
var title: String
var message: String
}
@State var details: Detail?
var body: some View {
MapReader { proxy in
Map(initialViewport: .camera(center: .dc, zoom: 10))
.mapStyle(.dark)
.onStyleLoaded { _ in
// This example uses direct style manipulation with MapboxMap
guard let map = proxy.map else { return }
try! setupClusteringLayer(map)
}
.onLayerTapGesture(Id.clusterCircle) { feature, _ in
details = Detail(queriedFeature: feature)
return true
}
.onLayerTapGesture(Id.point) { feature, _ in
details = Detail(queriedFeature: feature)
return true
}
.onMapTapGesture { context in
let latLon = String(format: "%.4f, %.4f", context.coordinate.latitude, context.coordinate.longitude)
details = Detail(title: "Map Tapped", message: "\(latLon)")
}
.ignoresSafeArea()
.alert(item: $details) {
Alert(title: Text($0.title), message: Text($0.message))
}
}
}
}
@available(iOS 14.0, *)
extension ClusteringExample.Detail {
init(title: String, message: String) {
self.title = title
self.message = message
}
init?(queriedFeature: QueriedFeature) {
guard let properties = queriedFeature.feature.properties else {
return nil
}
if case let .string(assetnum) = properties["ASSETNUM"],
case let .string(loc) = properties["LOCATIONDETAIL"] {
title = "Hydrant \(assetnum)"
message = "\(loc)"
} else if case let .number(pointCount) = properties["point_count"],
case let .number(clusterId) = properties["cluster_id"] {
title = "Cluster ID \(Int(clusterId))"
message = "There are \(Int(pointCount)) points in this cluster"
} else {
return nil
}
}
}
@available(iOS 14.0, *)
private func setupClusteringLayer(_ map: MapboxMap) throws {
// The image named `fire-station-11` is included in the app's Assets.xcassets bundle.
// In order to recolor an image, you need to add a template image to the map's style.
// The image's rendering mode can be set programmatically or in the asset catalogue.
let image = UIImage(named: "fire-station-11")!.withRenderingMode(.alwaysTemplate)
// Add the image to the map's style. Set `sdf` to `true`. This allows the icon images to be recolored.
// For more information about `SDF`, or Signed Distance Fields, see
// https://docs.mapbox.com/help/troubleshooting/using-recolorable-images-in-mapbox-maps/#what-are-signed-distance-fields-sdf
try! map.addImage(image, id: "fire-station-icon", sdf: true)
// Fire_Hydrants.geojson contains information about fire hydrants in the District of Columbia.
// It was downloaded on 6/10/21 from https://opendata.dc.gov/datasets/DCGIS::fire-hydrants/about
let url = Bundle.main.url(forResource: "Fire_Hydrants", withExtension: "geojson")!
// Create a GeoJSONSource using the previously specified URL.
var source = GeoJSONSource(id: "fire-hydrant-source")
source.data = .url(url)
// Enable clustering for this source.
source.cluster = true
source.clusterRadius = 75
let clusteredLayer = createClusteredLayer()
let unclusteredLayer = createUnclusteredLayer()
// `clusterCountLayer` is a `SymbolLayer` that represents the point count within individual clusters.
let clusterCountLayer = createNumberLayer()
// Add the source and two layers to the map.
try map.addSource(source)
try map.addLayer(clusteredLayer)
try map.addLayer(unclusteredLayer, layerPosition: LayerPosition.below(clusteredLayer.id))
try map.addLayer(clusterCountLayer)
}
@available(iOS 14.0, *)
private func createClusteredLayer() -> CircleLayer {
// Create a symbol layer to represent the clustered points.
var clusteredLayer = CircleLayer(id: Id.clusterCircle, source: Id.source)
// Filter out unclustered features by checking for `point_count`. This
// is added to clusters when the cluster is created. If your source
// data includes a `point_count` property, consider checking
// for `cluster_id`.
clusteredLayer.filter = Exp(.has) { "point_count" }
// Set the color of the circles based on the number of points within
// a given cluster. The first value is a default value.
clusteredLayer.circleColor = .expression(Exp(.step) {
Exp(.get) { "point_count" }
UIColor.systemGreen
50
UIColor.systemBlue
100
UIColor.systemRed
})
clusteredLayer.circleRadius = .constant(25)
return clusteredLayer
}
@available(iOS 14.0, *)
private func createUnclusteredLayer() -> SymbolLayer {
// Create a symbol layer to represent the points that aren't clustered.
var unclusteredLayer = SymbolLayer(id: Id.point, source: Id.source)
// Filter out clusters by checking for `point_count`.
unclusteredLayer.filter = Exp(.not) {
Exp(.has) { "point_count" }
}
unclusteredLayer.iconImage = .constant(.name("fire-station-icon"))
unclusteredLayer.iconColor = .constant(StyleColor(.white))
// Rotate the icon image based on the recorded water flow.
// The `mod` operator allows you to use the remainder after dividing
// the specified values.
unclusteredLayer.iconRotate = .expression(Exp(.mod) {
Exp(.get) { "FLOW" }
360
})
return unclusteredLayer
}
@available(iOS 14.0, *)
private func createNumberLayer() -> SymbolLayer {
var numberLayer = SymbolLayer(id: Id.count, source: Id.source)
// check whether the point feature is clustered
numberLayer.filter = Exp(.has) { "point_count" }
// Display the value for 'point_count' in the text field
numberLayer.textField = .expression(Exp(.get) { "point_count" })
numberLayer.textSize = .constant(12)
return numberLayer
}
@available(iOS 14.0, *)
struct ClusteringExample_Preview: PreviewProvider {
static var previews: some View {
ClusteringExample()
}
}
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