Have you ever walked on 39th Street between 5th and 6th Avenue and felt an otherworldly gravitational pull? Cory took the time to get to the bottom of this phenomenon: the sensation is a result of passing through the precise gravitational center of all the Starbucks coffee shops in Manhattan--
standing in that spot, you are equally close to EVERY SINGLE ONE! We know-- it blew our minds for the first half-hour-- but you'll eventually understand.
Benjamin has a much clearer explanation of the map down in the comments: the point is that the pull of Starbucks gravity is greatest at that point on 39th Street. To expand on that: if the island of Manhattan was a flat plate, and each Starbucks was a point of equal mass, and they were arrayed on the plate in positions corresponding to their geographical locations, the plate would balance at a point below the spot highlighted. Duh!