Mappr shows the most popular Foursquare venues; lets you check in with your favorite team

Mappr is a new local search site (and companion iPhone app) that uses Foursquare data to map the most popular venues in an area. Users can drill down by category to find the top bars, restaurants or shopping. And it adds a cool new feature: you can check in with your favorite team or find other people to join up with who are cheering for the same team.

To show off the team functionality, Mappr has launched with a “World Cup Edition” that lets you identify which team you’re rooting for when you check in. You can choose from any country participating in the World Cup. This lets other people know in real time where people are cheering for their favorite team on both the Mappr site and the iPhone app. You can even see which team has the most checkins on the leaderboard (no surprise: Team USA is leading by a healthy margin).

While the site is limited to World Cup teams right now, soon they intend to make the “teams” feature more free-form like Twitter hashtags, allowing you to add or join up with any group. With a simple search, you’ll know where your fellow fans are gathered to watch the game so you can meet up with them. It won’t be limited to sports teams, so you could identify with a corporation or a food-oriented interest group, for example, where you might be able to see where all the sushi lovers are eating right now.

Mappr shows the most popular venues in an area based on number of checkins. You’ll see larger icons for venues that have the most checkins and smaller icons for less popular venues. The icon size is relative to the venues in the current map view. Clicking an icon shows you more information about the venue, including tips and which teams are currently checked in.

You can see all the venues in an area or only the ones in certain categories. Mappr uses broad categories, like restaurants, nightlife or shops. Each venue is shown on the map by its (cheesy) category icon. Founder Bart Denny says in the future they hope to add more granular control, so you could choose to only show the top Chinese restaurants or karaoke bars, for instance.

The iPhone app offers most of the same features as the Mappr website, including popular venues, categories and teams. When you check in with Foursquare directly from the app you can choose which team you want to identify with. It includes shouts and will soon offer Facebook and Twitter sharing. Posts to Facebook will even include a special icon to show which team you’ve checked in with.

Mappr is built by Cartomapic. They’re currently using checkin data from Foursquare, but they’ve built a platform that will allow them to use data from other location based networks as it becomes available.

“I saw that there was going to be a great opportunity to build much better local search using these new social services’ signals. Reviews and ratings are great as far as it goes, but most people never bother. The checkin is such a better way of getting signals from the wider audience,” Denny says.

Right now, venues are ranked solely by number of checkins, but they hope to soon add your friends’ checkins into the ranking algorithm. “Then, it will really shine, as your friends’ favorite places are more visible. Your friends make the best maps,” Denny says.

The features Mappr has right now are incredibly useful for finding the most popular venues. The potential in their “teams” feature and adding friends checkins to the ranking algorithm are both exciting. It will add a whole new level of “socialness” to Foursquare.

Mappr is definitely one we’ll be keeping an eye on. Give it a spin and let us know what you think in the comments.