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Data Collection and Processing

We take a three-phase approach to releasing data about city-owned vacant land in which we progress from city data that can be outdated and incomplete to a living database that is more accurate and community-driven.

The first phase purely involves data and software that manipulates that data. We use the Local Law 48 of 2011 and the IPIS databases--both of which are published by the Department of Citywide Administrative Services--as a baseline and use the fields that describe the use of these lots (in IPIS, we use "RPAD_DESCRIPTION" and "Primary Use Text") to narrow down to the lots that are city-owned, vacant, and unused. Then we use a database of community gardens (created during the impressive 2010 GrowNYC community garden survey) to remove as many community gardens as we can--many say "community garden" under "Primary Use Text" field in the original databases, but some do not. Next we put these lots, which according to the most recent data available are vacant and city-owned, into our own database and put them on a map that only we can see.

The next phase is one that we might call a "virtual groundtruthing." We hire someone with experience with OASIS to use OASIS, satellite imagery, and Google Streetview to examine each lot individually. If the lot is found to be in use, a gutterspace, or inaccessible from the street, it is flagged accordingly in the database and either removed from the map or moved to a different layer on the map. Gutterspaces are slivers of land that can result surveying errors and other processes. They can be a one foot by one foot square of sidewalk or an inches-wide column of land between two lots, but either way they are unlikely to be usable for most purposes, so we move them to another layer on our map. This phase is very effective--in Brooklyn, for example, it eliminated over half of the original lots.

At this point, in areas where a lot of city-owned land has clearly recently been transferred (e.g. the Arverne-by-the-Sea area of Rockaway), a member of our team manually checks the transaction records on ACRIS to bring our information to the present by removing those lots that are no longer city-owned due to recent deed-transfers. In the Arverne-by-the-Sea case, this resulted in the removal of approximately 15 lots from the map of what is city-owned.

Finally, the database is published publicly online as a map, and real groundtruthing happens. Neighbors of lots write to us when we have lots mislabeled or missing, and we update the database accordingly. Sometimes neighbors also fill in the history of a lot--what used to be there, plans there had been for it--by adding notes to it. We sometimes visit neighborhoods with concentrations of vacant lots to hang signs on lots and start conversations with people who live there, and we update the database as needed--often by removing lots that have been built on, but sometimes also adding lots that are not in our database.

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