Mapping the planets of our solar system is usually best left to NASA, but don't tell that to Foursquare or Google. The two tech companies both have extra planets mapped. Back in 2005, Google added the Moon to their list of destinations. Celebrating the 35th anniversary of the moon landing, they teamed up with NASA to add a map of where the Apollo missions landed. It's not a complete map, but cut them some slack. Half of it is shrouded in complete darkness.
Today, the Mars Curiosity rover checked into Foursquare for the first time. "One check-in closer to being Mayor," Curiosity wrote. Again, Foursquare teamed up with NASA to make a map of the red planet highlighting where the different rovers have landed. (The Opportunity rover is peeved, by the way.)
The Moon's mayorship, if Foursquare was invented back when we still went regularly, would have gone to Apollo 17's Eugene Cernan and Harrison Schmitt. They spent the most time on the moon's surface, therefore they had more opportunities to check in.