It was confirmed today that Facebook has acquired Gowalla, and that the Gowalla service will close next month, but one thing is just as true while Gowalla still exists as it will be after it’s gone: Facebook and Foursquare lead the pack when it comes to the number of users who can check in at locations — by quite a lot.

Facebook isn’t strictly dedicated to location services like check-ins, but it has by far the largest audience of members who have access to its location features, which are now built into both its mobile and desktop versions. Facebook has a total of 800 million users, though not all of them use location services.

Previously, the location features were isolated in the “Facebook Places” section of the mobile application and website. The runner-up is Foursquare, but Foursquare is well ahead of the network that inhabits the #3 spot.

Foursquare’s team decided the Gowalla acquisition announcement would be an ideal time to reveal that the world’s second largest location-based social network has topped 15 million users — almost three times the number it had a year ago. In the ClickZ report on the milestone, Foursquare revealed that 50% of those users live in the United States.

Information about the location-based social networking landscape is concisely presented in the below infographic, which doesn’t yet reflect the new Foursquare numbers. It was originally published by Column Five Media. These stats can help you decide how best to plan your business or brand’s social media marketing strategy.

[Image credit: Nan Palmero]