MKAnnotationView, default MKPinAnnotationView, mapView:viewForAnnotation: delegate
MKMapRect, MKMapPoint, MKMapSize
MKMapRectForCoordinateRegion()
MKCoordinateRegionForMapRect()
MKMapPointForCoordinate()
MKCoordinateForMapPoint()

MKMapView:
-showAnnotations:animated:
-annotationsInMapRect: (using a QuadTree)
-visibleMapRect r/w property
-selectAnimation:animated:
selectedAnimations property

TODO: reuse annotation views, markers animation, map bounds animation.