From the New York Times:
Steve Rushin of Sports Illustrated has called the line running through Connecticut that separates Yankee fans and Red Sox fans the Munson-Nixon line. Mr. Rushin came up with the name — in honor of the late Yankee catcher Thurman Munson and the retired Red Sox right fielder Trot Nixon — in 2003, and he had to guess where the line ran: “north of New Haven but south of Hartford, running the breadth of central Connecticut.”
We don’t have to guess anymore.
Fans may not list which team they favor on the census, but millions of them do make their preferences public on Facebook. Using aggregated data provided by the company, the New York Times was able to create an unprecedented look at the geography of baseball fandom, going down not only to the county level, as Facebook did in a nationwide map it released a few weeks ago, but also to ZIP codes. We can now clearly see that both Hartford and New Haven are in fact Yankee outposts. We can also determine the precise Chicago neighborhoods where White Sox jerseys stop being welcome and the central California town where the Dodgers cede fan favorite status to the Giants.