Upper West Side. Meatpacking. Washington Heights. Little Italy. TriBeCa. This isn’t a story about Manhattan’s well-known neighborhoods. This is a story about the microdistricts within those neighborhoods — small commercial zones with an overabundance of similar businesses that only New York’s density could create.

A few weeks ago, as I walked to work in the Flatiron district of Manhattan, I noticed something unusual — not one, not two, but four tile stores, side by side, on 21st Street between Fifth and Sixth Avenue. Strange. Then, I remembered rumors about a magical street in Chelsea populated by dozens of flower nurseries. I already knew of Manhattan’s legendary Garment District. I wondered — how many microdistricts could there be in the city?