New York City has an open data policy, which makes it possible to download a number of interesting databases from the city government’s website. They’ve also put a number of data sets related to the built environment on a single map, at http://maps.nyc.gov/doitt/nycitymap/. I use it for various purposes in finding information about old buildings, but there is where I have to out one of those warnings that annoy people, like “Warning: coffee is hot” on coffee cups: there are problems with the data for buildings constructed before 1938. Just because the map says a building was constructed in 1920 doesn’t make it true. So check the results.
The picture above shows a piece of that map with my annotations on it. It is in west Harlem – technical Hamilton Heights, but that name is more popular with realtors than anyone else – in an area that was mostly, but not entirely, built up after the IRT subway opened in 1904. In short, it was north of the hot development areas in the 1880s and 1890s, but by 1905 or 1910 it was ripe for development and had a new and faster means of mass transportation than the elevated train over Amsterdam Avenue. The thing is, you can date the buildings simply by their footprints on the map. That’s what my annotations are for.
The red rectangle encompasses a few Old Law tenements, instantly recognizable by the narrow air shafts on their side lot lines. The pink rectangle has some pre-Old Law tenements form the 1870s, probably built in anticipation of the Ninth Avenue el being extended to Harlem. The 145th Street station, for example, opened in 1879. Pre-Old Law tenements lack even the minimal and unpleasant amenity of the air shafts.
The light-aqua rectangle encompasses a number of New Law tenements, constructed after the 1901 change to tenement regulation. The New Law required sizable light courts rather than just air shafts, and expanded the minimum size of rear yards. As a result, it became impractical to build tenements on single lots, since the 25-foot width of a standard lot didn’t allow for enough useable building after the side courts were subtracted. The H, O, and 8 plans that developed resemble apartment houses in much of Europe.
Finally, the purple rectangle encompasses a row of single-famiy houses.
Someone who knows how to manipulate large data sets – i.e., not me – could take the underlying data that makes up this map and identify buildings based solely on geometry. It wouldn’t be completely accurate – there’s not necessarily a difference in plan between a pre-Old Law tenement and a small industrial or commercial building – but it’s doable. People have been playing with these data sets in various ways, such as trying to answer the question of how many rowhouses there are in New York. It seems to me that the more data like this is made available, the more approaches we will have to analyze both the current built environment and its history.
Finally, given New Yorkers’ denial that Manhattan’s axis is not actually north-south, it’s refreshing that the city-created map shows the 29-degree tilt accurately.
