I had been interested in mapping my Foursquare checkins when I found Chris Mueller's Cartographer mapping library and thought its cluster maps offered some advantages over the obvious heatmap approach. I wrote 4mapper to try it out.

Once 4mapper was working I realized it would be fun to see other people's maps, so I put it on Google's appspot and added the ability to show other people your checkins.

You can try 4mapper at http://4mapper.appspot.com/.

When a user authorizes 4mapper to access their Foursquare account, it grabs their entire checkin history (and name and photo URL) and saves it. At no other time does it access your Foursquare account (the authorization tokens are stored in the user session, not in the database).

A user can mark their history as public, in which case they appear in the /users page, and their checkins can be mapped.

The module 4mapper uses to talk to the Foursquare API is available as a separate repository: foursquare-python.

The site doesn't work at all in Internet Explorer.

4mapper does not do a good job of translating errors into readable messages. Usually this comes up when a Foursquare API call times out, and the Google App Engine throws a DownloadError.

There is a bug in session logic that can result in a History record with a null history. The app doesn't deal with null histories well.

There's a Javascript error that pops up sometimes, too; If you see something about a "null bbox", something has gone wrong inside the Cartographer library.

It seems that Foursquare sometimes invalidates user photo URLs; Since 4mapper only updates that info when a user authorizes it, we can end up trying to show bad photo URLs on the /users page.

This is the closest thing to a webapp I've written in years, and it is my first Google AppEngine application. It's probably wrong.