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Nehad Ahmed fields the question day in and day out: What is that little tiled triangle carved into the sidewalk outside the smoke shop he manages in Greenwich Village?

The answer: It was once considered the smallest piece of private property in Manhattan.

The triangle is roughly 25 by 27 inches — smaller than a yield sign on a highway, or about 0.0000797113 of an acre. Not quite eight hundred-thousandths.

Mr. Ahmed said the triangle is one of those things that tour guides mention, along with what has long been known as the narrowest house in the Village, a nine-and-a-half-foot-wide structure at 75½ Bedford Street that has been home to famous residents, including Cary Grant, John Barrymore and the poet and playwright Edna St. Vincent Millay.

The triangle outside Mr. Ahmed’s smoke shop is completely covered by a plaque. People walk right over it. They stomp on it. They hopscotch around it. Or they do not notice it as they trudge toward the corner of Seventh Avenue South and Christopher Street — itself a triangle, Olympic-size by comparison and bracketed by sidewalks and two subway staircases less than 30 feet apart.