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Join data to vector geometry

Join local JSON data with vector tile geometries.

DataJoinExample.swift
import MapboxMaps
import UIKit
final class DataJoinExample: UIViewController, ExampleProtocol {
private var mapView: MapView!
private var cancelables = Set<AnyCancelable>()
override func viewDidLoad() {
super.viewDidLoad()
// Set up map and camera
let centerCoordinate = CLLocationCoordinate2D(latitude: 50, longitude: 12)
let camera = CameraOptions(center: centerCoordinate, zoom: 1.6)
let mapInitOptions = MapInitOptions(cameraOptions: camera, styleURI: .light)
mapView = MapView(frame: view.bounds, mapInitOptions: mapInitOptions)
mapView.autoresizingMask = [.flexibleHeight, .flexibleWidth]
view.addSubview(mapView)
// Add the data layer once the map has finished loading.
mapView.mapboxMap.onMapLoaded.observeNext { _ in
self.addJSONDataLayer()
// The following line is just for testing purposes.
self.finish()
}.store(in: &cancelables)
}
func addJSONDataLayer() {
// Create an array of countries and their HDI score
// Data: UN Human Development Index 2017 Europe extract
// Source: https://ourworldindata.org/human-development-index
struct Country {
let code: String
let hdi: Double
}
let countries = [Country(code: "ROU", hdi: 0.811),
Country(code: "RUS", hdi: 0.816),
Country(code: "SRB", hdi: 0.787 ),
Country(code: "SVK", hdi: 0.855 ),
Country(code: "SVN", hdi: 0.896 ),
Country(code: "ESP", hdi: 0.891 ),
Country(code: "SWE", hdi: 0.933 ),
Country(code: "CHE", hdi: 0.944 ),
Country(code: "HRV", hdi: 0.831 ),
Country(code: "CZE", hdi: 0.888 ),
Country(code: "DNK", hdi: 0.929 ),
Country(code: "EST", hdi: 0.871 ),
Country(code: "FIN", hdi: 0.92 ),
Country(code: "FRA", hdi: 0.901 ),
Country(code: "DEU", hdi: 0.936 ),
Country(code: "GRC", hdi: 0.87 ),
Country(code: "ALB", hdi: 0.785 ),
Country(code: "AND", hdi: 0.858 ),
Country(code: "AUT", hdi: 0.908 ),
Country(code: "BLR", hdi: 0.808 ),
Country(code: "BEL", hdi: 0.916 ),
Country(code: "BIH", hdi: 0.768 ),
Country(code: "BGR", hdi: 0.813 ),
Country(code: "MKD", hdi: 0.757 ),
Country(code: "MLT", hdi: 0.878 ),
Country(code: "MDA", hdi: 0.7 ),
Country(code: "MNE", hdi: 0.814 ),
Country(code: "NLD", hdi: 0.931 ),
Country(code: "NOR", hdi: 0.953 ),
Country(code: "POL", hdi: 0.865 ),
Country(code: "PRT", hdi: 0.847 ),
Country(code: "HUN", hdi: 0.838 ),
Country(code: "ISL", hdi: 0.935 ),
Country(code: "IRL", hdi: 0.938 ),
Country(code: "ITA", hdi: 0.88 ),
Country(code: "LVA", hdi: 0.847 ),
Country(code: "LIE", hdi: 0.916 ),
Country(code: "LTU", hdi: 0.858 ),
Country(code: "LUX", hdi: 0.904 ),
Country(code: "UKR", hdi: 0.751 ),
Country(code: "GBR", hdi: 0.922 )]
// Create the source for country polygons using the Mapbox Countries tileset
// The polygons contain an ISO 3166 alpha-3 code which can be used to for joining the data
// https://docs.mapbox.com/vector-tiles/reference/mapbox-countries-v1
var source = VectorSource(id: "countries")
source.url = "mapbox://mapbox.country-boundaries-v1"
// Add layer from the vector tile source to create the choropleth
var layer = FillLayer(id: "countries", source: source.id)
layer.sourceLayer = "country_boundaries"
// Build a GL match expression that defines the color for every vector tile feature
// https://docs.mapbox.com/mapbox-gl-js/style-spec/expressions/#match
// Use the ISO 3166-1 alpha 3 code as the lookup key for the country shape
let expressionHeader =
"""
[
"match",
["get", "iso_3166_1_alpha_3"],
"""
// Calculate color values for each country based on 'hdi' value
var green: Double
var expressionBody: String = ""
for country in countries {
// Convert the range of data values to a suitable color
green = country.hdi*255
expressionBody += """
"\(country.code)",
"rgb(0, \(green), 0)",
"""
}
// Last value is the default, used where there is no data
let expressionFooter =
"""
"rgba(0, 0, 0, 0)"
]
"""
// Combine the expression strings into a single JSON expression
// You can alternatively translate JSON expressions into Swift: https://docs.mapbox.com/ios/maps/guides/styles/use-expressions/
let jsonExpression = expressionHeader + expressionBody + expressionFooter
// Add the source
// Insert the vector layer below the 'admin-1-boundary-bg' layer in the style
// Join data to the vector layer
do {
try mapView.mapboxMap.addSource(source)
try mapView.mapboxMap.addLayer(layer, layerPosition: .below("admin-1-boundary-bg"))
if let expressionData = jsonExpression.data(using: .utf8) {
let expJSONObject = try JSONSerialization.jsonObject(with: expressionData, options: [])
try mapView.mapboxMap.setLayerProperty(for: "countries",
property: "fill-color",
value: expJSONObject)
}
} catch {
print("Failed to add the data layer. Error: \(error.localizedDescription)")
}
}
}
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