Fixed Points

There’s a fascinating but easily-solved problem when creating a set of drawings for a new building: defining where it should be built. We provide dimensions on our drawings for the size of the building, but how does a contractor know if it goes here or there? The answer, at least in a city, is to simply tie the dimensions for the building to the property lines. If the front facade of the building is 6 inches back from and parallel to the property line that separates the lot from the public street, that problem is solved (in one dimension, with a similar solution needed to tie the building down in the perpendicular direction, along the street). Of course, the solution raises a new question: how do we know where the property lines are?

The profession of surveying has been around a long time – much, much longer than structural engineering, if we define engineering as including rational analysis of structures – and it has various methods of measuring land and objects permanent affixed to the land. I recently started photographing examples of the interface between measurement and marking. Survey markers are permanent[efn_note]Well, as permanent as anything else we build, which is of variable intensity.[/efn_note] markers in the street to allow surveyors a starting point from which to measure structures. If a survey marker is known to be at a given location, then the lot lines can be found from that point and therefore buildings can be located from that point.

Here’s a good example to start with, from the northeast corner of Church and Leonard Streets in Tribeca:

Here’s a close-up so the text is clear:

I have no idea why the city’s topographic surveys fall under the jurisdiction of the five borough presidents rather than the mayor. I suspect it’s some holdover of organization from 100 or more years ago. I also suspect that the penalty for removal is to discourage the crowbar equivalent of joy-riding rather than any organized effort to mess with surveying. There’s a database that gives the registered location of each marker and this allows each to serve as a starting point for surveying.

In other words, “YOU ARE HERE.”

I’ve photographed a bunch of these of different types and will put up pictures in the coming days. (I’ve spent a lot for time walking around looking down as a result but have managed so far not to walk into any walls.) However, I’m only going to post permanent markers like the one above. Here’s a temporary marker, from the northeast corner of Hudson and Franklin Streets:

No disk, therefore no text, therefore not in the database. It’s more or less a big nail driven into the sidewalk. But it’s useful to the surveyors working on whatever project that was because they knew where it was relative to one of the permanent markers.