title: Showing and hiding groups of markers with Mapbox/LeafletJS
body: <p>I'm using MapboxJS to build a map. </p>
  
  <p>I currently give it a geoJson object of all my markers, which show up with no problem. </p>
  
  <p>As each point has a category, I'd like to add a control layer with checkboxes for each category, so users can show/hide each category. </p>
  
  <p>I've tried loading each marker individually into a layer but I'm getting mapbox errors. </p>
  
  <p>How should I approach this?</p>
  
  <p>Thanks in advance.</p>
  
  <p>Mei</p>