I thought I was so edgy, I checked in at the Starbucks on 181st street in Washington Heights and noted that I was at the northernmost Starbucks in the borough of Manhattan. How wrong I was, by two coffee shops and an interesting carto-historical technicality.
Like many Manhattanites, I was guilty of conflating the island of Manhattan, the borough of Manhattan, and the civilized world. Understandable, I'm sure you'll agree. But what gives about the most uptowniest Starbucks? Well, it turns out there are two Starbucks establishments in Marble Hill, a chunk of political Manhattan physically embedded in the Bronx thanks to the motion of history and the Harlem river.
If you look at maps closely, you'll see the border line. Marble Hill has a Bronx zip code and Bronx school district, but Manhattan representation. It used to be part of the island of Manhattan but was made an island by a canal and later joined to the Bronx by the infilling of the original course of the Harlem river. The more you know.
For extra credit, check out the excellently named Spuyten Duyvil Creek, anagrammed subway station maps (Damn Tyck Trees!), and Vanshnookenraggen's excellent subway map poster showing the Marble Hill stop on the 1.