North of the Triborough Bridge, the Harlem River slices sharply to the northwest, narrowing Manhattan Island down to a tadpole tail of land. At 142nd Street, Fifth Avenue, the dividing line between the East Side and the West Side, runs up against the river and comes to a stop. Lenox Avenue, which is Harlem's name for Sixth, extends northward as far as 147th, and then it, too, runs out of land. Seventh lasts all the way to 154th, just one block short of the Macombs Dam Bridge, which leads across the river to the Bronx and Yankee Stadium.
From the air, the triangle of land bordered on the south by 155th Street, on the west...