Location sharing social network Foursquare saw traffic to its site triple in the last two months since November, according to new numbers from traffic analyst firm Hitwise today. The service has seen unprecedented media coverage lately and is no doubt sending more updates to Facebook and Twitter, prompting the growth in visits back to Foursquare that Hitwise is measuring.

Foursquare announced a fascinating deal with Canadian newspaper chain Metro late last month that would deliver local editorial content to users depending on the locations they check-in from. We called that deal a sign that the era of location-as-platform has arrived.

Where was all this traffic to Foursquare coming from? Hitwise's Matt Tatham told us it broke down like this last month:

  1. Google sent 24% of this traffic and it's navigational not SEO. Most of this is probably from people who saw media coverage and Googled for the company's name.

  2. Twitter 21%

  3. Facebook 19%

Founder Dennis Crowley confirmed our assessment of the situation and said that the growth had been steady over time. "Usage growth looks more like a vert ramp than a hockey stick," he told us by email. Crowley was one of the founders of a location-based service called Dodgeball that was bought and then squandered by Google. This next attempt at the emerging world of location has been backed by a remarkable list of investors, including Twitter's Jack Dorsey, Digg's Kevin Rose, Delicious inventor Joshua Schachter, Ron Conway, Union Square Ventures and O'Reilly AlphaTech Ventures.

Foursquare is just one of many location-based social networks available but it's clearly growing fast. The service gives each user a user ID that's visible in their profile URL. A newly created test account we just set up was #354,317. If that's a roughly accurate estimate of the service's numbers, then Foursquare has doubled in registered users since mid-December.

Business review site Yelp came out with its version of mobile check-ins last month as well. Many people presume it's only a matter of time until Facebook moves into the location space, which will seriously shake that market up. Yahoo this week had a patent published for geo-located, social Augmented Reality. Location is hot.

We've got high hopes for a world of awesomeness built on top of platforms like these and Twitter's new location API, though adoption of that data has been surprisingly slow in uptake.

Why is location as a platform so exciting? Because it can be mashed up with other information. Among people hanging out at this coffee shop, what news stories are being read and shared the most today? (And who discovered those stories first?) You check-in at the local park a lot, would you like to read or perhaps contribute to the Wikipedia entry on it? These are the kinds of things that will become possible.

In the short term, it's just plain fun to check in on the internet from your favorite locations around town. "Where are you?" could become the new "what's on your mind?"

Watch this space for our forthcoming research report on mobile geolocation and our next public event, on trends in mobile development.