Create a heatmap layer

import Mapbox
 
class HeatmapExample: UIViewController, MGLMapViewDelegate {
 
override func viewDidLoad() {
super.viewDidLoad()
 
// Create and add a map view.
let mapView = MGLMapView(frame: view.bounds, styleURL: MGLStyle.lightStyleURL)
mapView.autoresizingMask = [.flexibleHeight, .flexibleWidth]
mapView.delegate = self
mapView.tintColor = .lightGray
view.addSubview(mapView)
}
 
func mapView(_ mapView: MGLMapView, didFinishLoading style: MGLStyle) {
// Parse GeoJSON data. This example uses all M1.0+ earthquakes from 12/22/15 to 1/21/16 as logged by USGS' Earthquake hazards program.
guard let url = URL(string: "https://www.mapbox.com/mapbox-gl-js/assets/earthquakes.geojson") else { return }
let source = MGLShapeSource(identifier: "earthquakes", url: url, options: nil)
style.addSource(source)
 
// Create a heatmap layer.
let heatmapLayer = MGLHeatmapStyleLayer(identifier: "earthquakes", source: source)
 
// Adjust the color of the heatmap based on the point density.
let colorDictionary: [NSNumber: UIColor] = [
0.0: .clear,
0.01: .white,
0.15: UIColor(red: 0.19, green: 0.30, blue: 0.80, alpha: 1.0),
0.5: UIColor(red: 0.73, green: 0.23, blue: 0.25, alpha: 1.0),
1: .yellow
]
heatmapLayer.heatmapColor = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:($heatmapDensity, 'linear', nil, %@)", colorDictionary)
 
// Heatmap weight measures how much a single data point impacts the layer's appearance.
heatmapLayer.heatmapWeight = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:(mag, 'linear', nil, %@)",
[0: 0,
6: 1])
 
// Heatmap intensity multiplies the heatmap weight based on zoom level.
heatmapLayer.heatmapIntensity = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:($zoomLevel, 'linear', nil, %@)",
[0: 1,
9: 3])
heatmapLayer.heatmapRadius = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:($zoomLevel, 'linear', nil, %@)",
[0: 4,
9: 30])
 
// The heatmap layer should be visible up to zoom level 9.
heatmapLayer.heatmapOpacity = NSExpression(format: "mgl_step:from:stops:($zoomLevel, 0.75, %@)", [0: 0.75, 9: 0])
style.addLayer(heatmapLayer)
 
// Add a circle layer to represent the earthquakes at higher zoom levels.
let circleLayer = MGLCircleStyleLayer(identifier: "circle-layer", source: source)
 
let magnitudeDictionary: [NSNumber: UIColor] = [
0: .white,
0.5: .yellow,
2.5: UIColor(red: 0.73, green: 0.23, blue: 0.25, alpha: 1.0),
5: UIColor(red: 0.19, green: 0.30, blue: 0.80, alpha: 1.0)
]
circleLayer.circleColor = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:(mag, 'linear', nil, %@)", magnitudeDictionary)
 
// The heatmap layer will have an opacity of 0.75 up to zoom level 9, when the opacity becomes 0.
circleLayer.circleOpacity = NSExpression(format: "mgl_step:from:stops:($zoomLevel, 0, %@)", [0: 0, 9: 0.75])
circleLayer.circleRadius = NSExpression(forConstantValue: 20)
style.addLayer(circleLayer)
}
}