title: How often is drawMapRect:zoomScale:inContext: supposed to be called?
body: <p>I have a custom MKOverlayRenderer. I add an MKOverlay (also custom) to the MKMapView after the first region change (when it moves from the default location to the user's). The rendering speed was pretty laggy, so I logged the function calls.</p>
  
  <pre><code>2016-07-20 14:03:21.486 MyApp[360:38679] mapView:regionDidChangeAnimated:
  2016-07-20 14:03:22.351 MyApp[360:38679] addOverlay:level:
  2016-07-20 14:03:22.353 MyApp[360:38679] mapView:rendererForOverlay:
  2016-07-20 14:03:22.460 MyApp[360:38709] drawMapRect:zoomScale:inContext:
  2016-07-20 14:03:22.460 MyApp[360:38706] drawMapRect:zoomScale:inContext:
  2016-07-20 14:03:22.501 MyApp[360:38709] drawMapRect:zoomScale:inContext:
  2016-07-20 14:03:22.504 MyApp[360:38706] drawMapRect:zoomScale:inContext:
  2016-07-20 14:03:22.504 MyApp[360:38707] drawMapRect:zoomScale:inContext:
  2016-07-20 14:03:22.560 MyApp[360:38707] drawMapRect:zoomScale:inContext:
  2016-07-20 14:03:22.562 MyApp[360:38709] drawMapRect:zoomScale:inContext:
  2016-07-20 14:03:22.582 MyApp[360:38713] drawMapRect:zoomScale:inContext:
  </code></pre>
  
  <p>This is without touching the device. Is drawMapRect:zoomScale:inContext supposed to be called repeatedly like this?</p>