Tells the delegate that the specified map view is about to retrieve some map data.
- iOS 3.0+
- macOS 10.9+
- tvOS 9.2+
The map view that began loading the data.
This method is called whenever a new group of map tiles need to be downloaded from the server. This typically occurs whenever you expose portions of the map by panning or zooming the content. You can use this method to mark the time that it takes for the map view to load the data.