A working sample to GoogleMaps SDK, for downloading and binding images from a specific `URL` to a `GMSMarker`

GoogleMapsViewController.swift

//
//  GoogleMapsViewController.swift
//
//  Created by Erid Bardhaj on 8/20/18.
//  Copyright © 2018 Erid Bardhaj. All rights reserved.
//

import UIKit
import GoogleMaps

class GoogleMapsViewController: UIViewController {
    
    // MARK: - Properties
    // MARK: Immutable
    
    private let camera = GMSCameraPosition.camera(withLatitude: -33.86, longitude: 151.20, zoom: 12.0)
    private lazy var mapView = GMSMapView.map(withFrame: .zero, camera: camera)
    
    // MARK: - Overrides
    
    override func loadView() {
        view = mapView
        
        createMarkers()
    }
    
    // MARK: - Actions
    
    func createMarkers() {
        let mapCoordinates: [CLLocationCoordinate2D] = coordinates()
        let iconURLs: [URL] = imageURLs()
        
        for i in 0..<mapCoordinates.count {
            let imageURL = iconURLs[i]
            
            let marker = GMSMarker()
            marker.position = mapCoordinates[i]
            marker.map = mapView
            applyImage(from: imageURL, to: marker)
        }
    }
    
    // MARK: - Helpers
    
    func applyImage(from url: URL, to marker: GMSMarker) {
        DispatchQueue.global(qos: .background).async {
            guard let data = try? Data(contentsOf: url),
                let image = UIImage(data: data)?.cropped()
                else { return }
            
            DispatchQueue.main.async {
                marker.icon = image
            }
        }
    }
    
    // MARK: Content
    
    func coordinates() -> [CLLocationCoordinate2D] {
        let location0 = CLLocationCoordinate2D(latitude: -33.86, longitude: 151.20)
        let location1 = CLLocationCoordinate2D(latitude: -33.88, longitude: 151.20)
        let location2 = CLLocationCoordinate2D(latitude: -33.90, longitude: 151.20)
        let location3 = CLLocationCoordinate2D(latitude: -33.86, longitude: 151.22)
        let location4 = CLLocationCoordinate2D(latitude: -33.86, longitude: 151.24)
        let location5 = CLLocationCoordinate2D(latitude: -33.86, longitude: 151.26)
        
        return [
            location0,
            location1,
            location2,
            location3,
            location4,
            location5
        ]
    }
    
    func imageURLs() -> [URL] {
        let url0 = "https://wallpaperbrowse.com/media/images/3848765-wallpaper-images-download.jpg"
        let url1 = "https://cdn.pixabay.com/photo/2016/10/27/22/53/heart-1776746_960_720.jpg"
        let url2 = "https://images.pexels.com/photos/34950/pexels-photo.jpg?auto=compress&cs=tinysrgb&h=350"
        let url3 = "https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRZjVLtJDgMTOExfMHsTZuT4G5cAmaRT0N0vnoVbblrTTKkwSOb"
        let url4 = "https://www.bmw-me.com/content/dam/bmw/common/all-models/m-series/m4-convertible/2017/images-and-videos/images/BMW-m4-convertible-images-and-videos-1920x1200-06.jpg.asset.1510607725528.jpg"
        let url5 = "https://wallpaperbrowse.com/media/images/maxresdefault_RlXh3Bt.jpg"
        
        return [
            url0,
            url1,
            url2,
            url3,
            url4,
            url5
            ].map { URL(string: $0)! }
    }
}

// MARK: - Extensions

extension UIImage {
    
    func cropped() -> UIImage? {
        let cropRect = CGRect(x: 0, y: 0, width: 44 * scale, height: 44 * scale)
        
        guard let croppedCGImage = cgImage?.cropping(to: cropRect) else { return nil }
        
        return UIImage(cgImage: croppedCGImage, scale: scale, orientation: imageOrientation)
    }
}