16 is the product of squaring four, so naturally the date of April 16th is the most logical one to be called Foursquare Day. Just why such a celebration should exist is less obvious. As it turns out, a grassroots movement of Foursquare users built up steam around the idea of dedicating a day to the online check-in service, that concept then filtered through to Foursquare's founders who decided to go "100% in on this," and now, somewhat surprisingly, so has New York City Mayor (the
