"The greatest evil which ever befell New York City was the division of the blocks into lots of 25 x 100 feet. So true is this, that no other disaster can for a moment be compared with it. Fires, pestilence, and financial troubles are as nothing in comparison; for from this division has arisen the New York system of tenement-houses, the worst curse which ever afflicted any great community." -The New York Tenement-House Evil and Its Cure
A prohibition on alleys, however, required that all blocks be fairly narrow, since interior block space in wide blocks, without alley access, would be distant from the street and have little economic value. But the commissioners could not go too narrow either: due to the minimum street width requirements, a city with square blocks much less than 200' would have as much as 50 percent of its land area occupied by streets – a poor outcome for commissioners concerned with maximizing the amount of land for sale to private buyers.
The resulting blocks of 200 x 800 were therefore an awkward compromise, as an attempt to keep blocks narrow enough such that the amount of inaccessible interior block space was minimized, while maximizing the ratio of buildable to non-buildable area by stretching the blocks out lengthwise. In no other American city are similar blocks found, possibly due to the fact that in all, or nearly all other cities, alleys were not prohibited and could be called upon to open up overly large grid blocks.
Following the establishment of the initial plan, blocks were subdivided into individual lots by property owners, with a common dimension being 25' x 100'. Although Flagg writes that "[w]hen the city was first laid out, the division of the blocks into lots 25 x 100 ft. was entirely unobjectionable," as "people generally built houses of moderate dimensions, lighted at the front from the street, and in the rear from the yard," once land values rose – which did not take long – the deep lot provided a strong enticement to construct houses in the rear, notwithstanding the lack of street access. Pre-law tenements soon followed, making the most profitable use of the blocks which the city had parceled out in the thousands to private developers. The lot sizes, moreover, although presumably laid out with a single family in mind, actually contained an inherent bias against single family homes: since a rowhouse might only need 40' or 50' of depth, the creation of lots of 100' length, while prohibiting alleys, essentially made the construction of modest rowhouses an uneconomical proposition.
|San Francisco street map, showing narrow streets bisecting|
grid blocks and reducing block widths to 150' and in some
cases as little as 100'.