by Ben Blatt

A version of this post can be read in the Wall Street Journal here.

Like all sports rivalries, picking a side in the Red Sox-Yankee rivalry is almost entirely geographic. Everyone knows as you drive through the traffic-filled highways of Connecticut, bumper stickers will slowly fade from those supporting the Sox to those supporting the Yanks. But exactly where is the border between the two fanbases? Although others have tried to answer this before, by using data from the 2.5 million people in New York or New England that ‘like’ either the Red Sox or Yankees I was able to create a more accurate rivalry map than ever before.

To figure out where the true boundaries are I used Facebook’s ‘Create and Ad’ feature. By pretending be buying an advertisement, Facebook will tell you the approximate number of people in an area who ‘like’ something. For instance there are 101,400 people in Boston who like the Red Sox (of which, 280 are also 18-year old males who also ‘like’ Justin Bieber).

I went through towns in New England and New York to determine the percentage of people who like the Red Sox versus the Yankees. Using this data I was able to trace out the borders of the two fanbases. Below is the final map.

Surprisingly (or possibly unsurprisingly) the borders of Massachusetts and Vermont turned out to be the actual borders of the two rivals. I had thought it was possible that Red Sox Nation might extend into northern New York or Yankee territory might extend into Vermont. This turned out not to be the case. Check out the map below of the border between western Massachusetts and New York as an example of how pronounced fanbases change on different sides of a state border (Note: For some of the towns their populations were combined for the graph below because they were too small otherwise to get accurate data).

The true battleground is, of course, Connecticut. Looking at the raw data we see the state is very mixed.

With the exception of a few outliers, towns in the Northeast (and especially those towns which border Massachusetts or Rhode Island) have a high concentration of Sox fans. Towns in the Southwest (especially the towns that border New York) have a high concentration of Yankees fans.

Drawing a border through Connecticut using the map above and the data was not easy. I decided that a border should be contiguous. This made it impossible to group all the Sox-leaning towns on one side and all Yankee-leaning towns in the other. The border I came up with is below. There are several other borders that could have been drawn that would have been similarly accurate. My border tried to maximize the number of towns with more than 50% Sox fans on the Red Sox side and the number of towns with more than 50% Yankee fans on the Yankee side.

If you click to view the map you can see which towns lay on the border. This border differs significantly from the map that John Branch created in his New York Times article ‘Where Do Rivals Draw the Line’ . His map plunges the border of Red Sox Nation much farther into western Connecticut and cedes the major city of Hartford to the Sox. According to the Facebook data I was working off of, Hartford is 57% Yankees fans, a decided advantage. I think my map is able to command accuracy far greater than the Times article (which was based on driving around towns and surveying strangers) or other methods. Facebook provides a survey with an unprecedented sample size.

Just in case you are a big Connecticut geography nut, I have attached the same shaded map as before but with the towns labeled. Also below is a ranking of each town in Connecticut in order of the highest to lowest proportion of Red Sox fans (some towns were left off the list because they were too small and did not have enough data. For the map an average of the surrounding towns was used).

The towns above are highlighted based on whether or not they were grouped into Red Sox or Yankee territory on the map. You can see that many towns had more than 50% of one fanbase but were put in the other’s territory. While you could play around with the borders more, there are many places where it would be impossible to draw a contiguous border and not have any outliers like this.

While I don’t think any of the results above are groundbreaking there was one result that surprised me the most throughout this research: there are 262,500 people who ‘like’ both the Red Sox and the Yankees. If only I had time, I would map out where they live so that every true baseball fan can avoid them.

Ben Blatt can be contacted at bbblatt@gmail.com.