Since the Washington Nationals arrival to D.C. in 2005, the split between Nats and Baltimore Orioles fans in the Greater Washington region has been dramatic.
Earlier this season, the New York Times released a study that shows exactly where fan allegiances lie based on geographic location.
Using "aggregated data provided by [Facebook]," 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."
Ahead of today's opening game in the Battle of the Beltways, here's where the Nationals and Orioles are popular in the region.
Unsurprisingly, the Nationals dominate the scene around the Potomac River, covering big parts of Montgomery County, Prince George's County and Northern Virginia.
Orioles fans maintain a stronghold on Northern Maryland and the Eastern Shore.
See a more detailed version of the map below:
Interestingly enough, the Nationals and Orioles are not the second favorite team of many people in the region. That distinction belongs to the Boston Red Sox and New York Yankees.