By Jason Barr with Gerard Koeppel
In 1609, when Henry Hudson sailed up the river that now bears his name, he saw an island forest covered in oak, pine and tulip trees. Two centuries later, in 1811, when the grid plan was enacted, most of Manhattan was still undeveloped. In fact, the footprint of the city itself encompassed only 1.3 square miles at the lower tip. The rest was quite sleepy - farms, country estates, and pockets of unspoiled nature.
When the grid plan was being conceived, it was a visionary notion that someday nearly the entire island would be transformed into a global metropolis. There were no automobiles or railroads, and steamboats were still a strange curiosity. The average person was dependent on her own two feet or a horse for transportation. Visiting a friend in Harlem Heights from the city was a three-hour journey.
As discussed in a previous post, the Commissioners specified very little in the plan, only presenting a map of streets and blocks. Looking at the two-dimensional map created by John Randel, Jr. (right) gives the impression that from the tabula rasa of rural New York urban order was created. But that was not true at all.
The plan said nothing about street grades or how the grid and topography were to work together… or not. Rather, as the mandated streets started to appear, road slopes would be determined piecemeal, based on the need to facilitate transportation by keeping elevation changes minimal. As streets were opened, if a landowner found he was above or below the grade, he was forced to go down or build up, often at considerable cost, to match his lot with the street. In the 27 years from 1830 to 1856, the nearly 200 openings of road segments or public squares placed a heavy burden on property owners, who were also assessed to pay for the new streets themselves (but compensated for the loss of their lands taken for the streets).
The map suggests that rather than a great leveling, the island was subject to a great smoothing. In fact, about two-thirds of all blocks had changes of less than 10 feet, and 40 percent of the blocks had average elevation changes of less than 5 feet. The modal change was to add between 0 and 10 feet; much of this was also due to infill along the riverbanks. Nearly as much of the island was “brought up” as it was “brought down.” Valleys needed to be filled in, while the hills were lowered. The average change across all blocks, in fact, was increase of elevation of 1.7 feet.
This is also confirmed by a statistical analysis, which looks at what variables drove the average change in the elevation of each block. These control variables included the starting elevation in 1609, whether there was a stream on the block, or whether the area was formerly wetlands. In short, higher elevation blocks were reduced, on average, by 1.5 foot per 10 feet rise in elevation. If an area was a wetland, its elevation was increased, on average, by about 3.4 feet.
Despite the images of the houses perched on rocky hills surrounded by the newly created streets several feet below, the data suggest that this was not the norm across Manhattan. Today the general topography remains the same as it did in 1609; the Battery is prone to flooding from storm surges and Bennet Park, at 183rd Street, is still the island’s highest point, but the transition from south to north is much more evenly gradual.