Visualizing Meetup.com RSVP data on a map

For our last streaming example, we're going to connect our web frontend to the public streaming API of Meetup. With Meetup, people can easily schedule meetups with people that share interests. An interesting aspect of Meetup is that it offers a publicly available WebSocket endpoint which provides RSVP information on public meetings. When we connect to that endpoint, we get information back which looks like this:

Each message is a single RSVP from someone either wanting to attend a meeting, or someone letting the organizers know they won't attend. When we look a bit closer at the JSON message, we see a lot of useful information:

{ 
  "venue": { 
    "venue_name": "The Moon Under Water (Wetherspoons)", 
    "lon": -0.74885, 
    "lat": 52.04258, 
    "venue_id": 995244 
  }, 
  "member": { 
    "...