To compare maps, long press (about half a second) in either map to center the maps on the area you want to view.
In order for the app to work, you must install Mapbox iOS SDK to the project. To install using Cocoapods, follow the directions on the Mapbox website: https://www.mapbox.com/guides/first-steps-gl-ios/#cocoapods
In Terminal, change the directory to your project’s root folder and then run the command:
pod install
Also, you must enter your Mapbox Access Token from your Mapbox account page (see the warning directive in ViewController.m).
To learn more about the app, see my post: http://charlesgrier.com/mapboxgl/