Data-driven circles

Source data originates from a GeoJSON file uploaded to create a tileset in Mapbox Studio. Refer to the Working with GeoJSON data guide for more information about working with GeoJSON source data.

Learn more about creating data visualizations in our Predicates and expressions guide.

import Mapbox
class ViewController: UIViewController, MGLMapViewDelegate {
var mapView: MGLMapView!
override func viewDidLoad() {
super.viewDidLoad()
// Create a new map view using the Mapbox Light style.
mapView = MGLMapView(frame: view.bounds)
mapView.styleURL = MGLStyle.lightStyleURL
mapView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
mapView.tintColor = .darkGray
// Set the map’s center coordinate and zoom level.
mapView.setCenter(CLLocationCoordinate2D(latitude: 38.897, longitude: -77.039), animated: false)
mapView.zoomLevel = 10.5
mapView.delegate = self
view.addSubview(mapView)
}
// Wait until the style is loaded before modifying the map style.
func mapView(_ mapView: MGLMapView, didFinishLoading style: MGLStyle) {
// "mapbox://examples.2uf7qges" is a map ID referencing a tileset. For more
// more information, see mapbox.com/help/define-map-id/
let source = MGLVectorTileSource(identifier: "trees", configurationURL: URL(string: "mapbox://examples.2uf7qges")!)
style.addSource(source)
let layer = MGLCircleStyleLayer(identifier: "tree-style", source: source)
// The source name from the source's TileJSON metadata: mapbox.com/api-documentation/#retrieve-tilejson-metadata
layer.sourceLayerIdentifier = "yoshino-trees-a0puw5"
// Stops based on age of tree in years.
let stops = [
0: UIColor(red:1.00, green:0.72, blue:0.85, alpha:1.0),
2: UIColor(red:0.69, green:0.48, blue:0.73, alpha:1.0),
4: UIColor(red:0.61, green:0.31, blue:0.47, alpha:1.0),
7: UIColor(red:0.43, green:0.20, blue:0.38, alpha:1.0),
16: UIColor(red:0.33, green:0.17, blue:0.25, alpha:1.0)
]
// Style the circle layer color based on the above stops dictionary.
layer.circleColor = NSExpression(format: "mgl_step:from:stops:(AGE, %@, %@)", UIColor(red:1.0, green:0.72, blue:0.85, alpha:1.0), stops)
layer.circleRadius = NSExpression(forConstantValue: 3)
style.addLayer(layer)
}
}