Streaming Foursquare checkins with Google Maps

This Saturday was the second annual Redline Challenge which is a bar crawl from Downtown Crossing to Davis Square that loosely tracks the MBTA Redline.

This year, we decided to use Foursquare to allow the website to track the position of several of the participants on the challenge. Foursquare natively allows you to track your checkin history with private URLs. Currently, they support a handful of formats with KML being the most interesting for our purposes. You can find your private URLs by navigating to

We used the Google Maps API along with the KML stream from Foursquare to dynamically place markers on the map as different users checked in to different venues.

Here is the PHP we used to pull back the KML feed, transform it to JSON, and spit it back to our jQuery on the client side:

Pretty straight forward. Here is the jQuery code on the client side to add markers to the map:

That’s about it.