Foursquare has produced a map of the last 500M check-ins on its service, gathered over the last three months. The map, which you can check out in its full glory here, doesn’t just display the points at which users have checked in to places, though. It also shows the connections that have allowed it to build a personalized recommendation service that rivals Yelp.

Foursquare’s approach to this has been somewhat unique in this arena. Rather than setting out to ask people to rate locations and write reviews from the beginning, it simply gave them a game to play. They checked in, they got badges in return and a history of where they’ve been. Over time, Foursquare evolved that product into what it is now: a powerful recommendation engine that is supremely aware of your location, your likes and the places that are most likely to appeal to you and your friends.

Recently, a ratings system was added to the site, but instead of letting users arbitrarily tap a number, Foursquare assigns them based off of a bunch of signals to deliver a personal rating. In the future, the rating that Foursquare gives you, and the one it gives a friend for a the same restaurant may be very different.

Screen Shot 2013 01 17 at 2.59.28 PM 730x352 Map of 500M Foursquare checkins demonstrates how they built a Google PageRank for the real world

In a blog post today, Foursquare says that it likes to think of its recommendation system as a “Google PageRank for the real world.” The PageRank system is a closely guarded algorithm that determines the worth of pages based off of a bunch of mutable and constantly-being-tweaked factors. That worth valuation is what surfaces one link over another when you plug something into a Google Search box.

Delivering that kind of weighted personal recommendation based on what was originally a game is what continues to impress me about where Foursquare is taking its product.

There’s also a nod to the business aspects of things. “If you like a cafe in your neighborhood, or a boutique shoe store, we want to build tools so they can keep you up to date with their latest menu items, shipments, and sales. And if you’re looking for a museum to go to this weekend, we want them to be able to share their latest exhibits and special admission hours with you.”

Obviously, that can add some value to the user, but it also offers some strong monetization possibilities, something that Fourquare sorely needs if it’s going to get over the hill into its next growth cycle. Of course, there’s always the possibility that Apple will just buy or integrate them.