Today the New York Times' new Upshot site published a very cool series of graphics that use Facebook data to chart the most popular Major League Baseball team in every zip code in the country. Here is the section on New York:
It's all gray because every single zip code had more Yankees fans than Mets fans. Including the ones immediately surrounding the Mets' stadium. Though there is the possibility that Mets fans simply don't sign up for Facebook at the same rate as Yankee fans (because the debilitating long-term sadness makes it unbearably difficult to interact, even online, with other humans).