title: Hiding map annotations without deleting them
body: <p>Using a MKMapView I have a pile of annoatations loaded onto it and I want to be able to filter the annotations displayed with a segmented control.</p>
  
  <p>I'm using custom annotations with a type variable so I can tell them apart from one another but I haven't been able to find a way to hide and display a subset of annotation views at will.</p>