When Colin Hagendorf set out to eat every pizza in New York City, he had no easy way of knowing that there are more than 1,600 restaurants officially classified as pizzerias across the five boroughs -- more than every other type except Chinese and the vague catch-all category of "American" eateries, according to a city health-inspection database.

Trying every iteration of the New York slice turned out to be more than a determined pizza hound could handle, as the Journal explains in a profile Wednesday, so Hagendorf limited...