The Rise and Fall of Manhattan’s Densities (1800-2010)

by Shlomo Angel and Patrick Lamson-Hall

Abstract: Using a novel methodology, we study the changes in the population densities of the built-up areas of Manhattan and its neighborhoods from 1800 to 2010. Built-up areas were determined from historical maps, insurance maps, and air photographs, while population data were collected for census wards from 1790 to 1910 and for census tracts thereafter. We found that densities remained stable, at 200 persons per hectare, until 1840 when the growth in the built-up area could no longer keep up with rapid population growth. By 1910, average densities in Manhattan were triple those of 1840, while average densities in some neighborhoods were twice as high and more. Densities then started to decline, largely due to three public actions: the annexation of Brooklyn, Queens, the Bronx and Richmond County to Manhattan in 1898; the creation of vast new areas for urban expansion in the 1900 Topographical Bureau plan; and the building of the subway system from 1904 onwards. These actions led to the rapid decongestion of Manhattan’s overcrowded neighborhoods, as lower-income workers suburbanized while still commuting to Manhattan on a nickel fare. Densities in Manhattan declined until 1980 and have risen slightly since. New York City is now expecting a significant increase in population, entailing significant densification in Manhattan and elsewhere. Using the lessons learned from our study, we outline a densification program that could accommodate a larger population without recourse to heavy-handed land assembly for large and heavily subsidized housing projects. Our strategy is based on our conviction that we can achieve a more efficient, more equitable, and more sustainable densification in New York City with small actions on the part of the many than with big actions on the part of the few.

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