Loading GeoJSON and drawing a polyline

In this recipe, you will learn how to parse a GeoJSON file and draw a polyline on the map using Mapbox GL. This will be a great start if your purpose is to create applications that draw routes on a map.

How to do it…

Perform the following steps:

1. Open the Chapter6-Recipe6-Begin folder and then the .xcworkspace file. This project contains a basic Mapbox GL map. It uses the emerald style, which is the best-looking style to display directions. The project also contains a route.geojson file. Normally, you would fetch the data from a service, but for the purpose of this recipe, we will use a file stored in our bundle.

2. Our first step is to parse the GeoJSON file and get the coordinates contained in the geometry.coordinates array under the features. We will do this in a separate method, as follows:

   - (void)loadGeoJSONFile {
   
       dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
   
       dispatch_async(queue, ^{
   
           NSString...