Tile Overlays in iPhone App

There is a webpage I am looking at that displays a Google Map (via javascript), but certain areas of the map have an overlay (textures appear different than the rest of the map, etc.). From what I can gather, this is done on the webpage via a getTileURL function, which depends on the zoom level and current coordinate.

I am interested in portraying this same overlay 开发者_如何学Pythonin my iPhone application, which currently has a mapView set up. Is there anyway to implement the same sort of getTile function in objective-c for a mapView?

If someone could please provide some sample code or point me in the right direction I would greatly appreciate it. Thank you.