title: How to filter annotations on a map view
body: <p>I'm currently working on an application that displays annotations on the map. They have multiple colours that represent different things. For example green represents cafes and Purple is to represent museums. I would like to be able to have a button that filters the annotations so that all the purple show whilst the other colours stay hidden and vice versa.</p>
  
  <p>Thanks in advance, Niall.</p>