Issue link: https://read.dmtmag.com/i/117518
an increased demand for new GIS data and a proven source of labor to produce them. The last piece of the puzzle came in 2011 with the 50th anniversary of the 1961 zoning resolution. What better time could there be to start the project? Re-Creating 1961 Zoning From the start, this was envisioned as a three-phase project. The first phase would be the creation of the baseline zoning, as established by the 1961 Zoning Resolution on Dec. 15, 1961. The second phase would involve the addition of all the historical zoning changes in the chronological order they occurred. The polygon data collected during the initial scanning of the historical zoning maps, from changed areas on the maps, would provide the dates and extents of the rezoned areas. This timeline would dictate the sequential order in which zoning changes would be added. Finally, the completed historical zoning data would be merged with current zoning data to create a complete zoning GIS encompassing the current state of zoning and an unbroken historical path back to 1961. The actual workflow for creating the 1961 zoning was conceptually simple. Starting with a copy of current GIS data, zoning districts and commercial-overlay districts, the georeferenced historical zoning maps were used as a reference source to edit the current GIS data "back" to their original 1961 state. An enterprise GIS database was used to manage the editing process, which allowed distribution of the editing workload over multiple, simultaneous editors. Although editing in a geodatabase environment provided the added benefit of conflict resolution, a further step was taken to avoid conflicts among editors by splitting the data into individual zoning map units. Editors selected the maps they wished to update and worked their way through them, making visual comparisons of the current GIS zoning and commercial-overlay district polygons superimposed over georeferenced 1961 zoning maps. Edits were made to match the original state of the zoning as shown on each 1961 map. A "cut and merge" methodology was used for editing polygons, which proved effective, easy to teach and efficient. Edits consisted mainly of merging groups of smaller zoning-district polygons into larger ones; in 1961, there were only 58 unique zoning-district designations, while in 2013, there are now 157. Further, this methodology avoided topological errors such as overlaps or gaps among neighboring features that can result from other editing methods. After the zoning districts were complete, the process was repeated for the commercial-overlay districts. Some other subtleties were encountered along the way, such as the changes since 1961 in city park areas, which have no zoning, and changes to official city streets, which are used to define zoning districts. Both affect A map demonstrates an area where zoning in 1961 (black lines) was much simplified compared with today's zoning (in color). zoning-district areas and boundaries, and they needed to be accounted for. Finally, the zoning map "units" were merged back together into continuous citywide layers, and the 1961 zoning data were complete. Where We Are Now The completed 1961 zoning dataset now is in an initial period of internal use and evaluation by agency planners. After the department is comfortable internally with the data's accuracy, they will be made available to the general public as a downloadable data source and an addition to ZoLa, the department's Web-mapping application. With the baseline 1961 zoning data now complete, the project's second phase, the addition of all subsequent (1961-2007) zoning changes, has begun. Completion of this second phase will result in two separate datasets encompassing the city's entire zoning history back to 1961. Looking forward into the project's future, options for merging the completed historical data into the current zoning GIS and the potential uses this completed spatialtemporal data have online are under consideration. Although there haven't yet been any solicitations for movie or book rights to this zoning-themed time-travel adventure, who can say what the future will hold? Chris Rado is CAD-GIS team leader, Technical Review Division, New York City Department of City Planning; e-mail: c_rado@planning.nyc.gov. Uttam Bera is project manager/GIS specialist, Information Technology Division, New York City Department of City Planning; e-mail: u_bera@planning.nyc.gov. M A R C H 2 O 1 3 / W W W . G E O P L A C E . C O M 17