For our TEN & TALLER project – representing all of the buildings erected in Manhattan from 1874 through 1900 that were ten stories or taller – the Museum created a map interface that merges a historic Bromley fire insurance map and a modern map we created using sets of geographical data from the NYC Department of City Planning. A slider allows viewers to transition the base map from the present to the past and vice versa. Over these maps, we added the footprints of the 249 buildings in the TEN & TALLER STUDY, color-coded by use.
The simple zoomed-out modern map emphasizes the spatial geography and different use types of our buildings. Using the “Year Built” slider will add or remove buildings by date to dramatize the pace of development. For example, sliding the button between 1897 and 1900 will reveal a burst of construction that outline the path of Broadway.
The historic map adds color and details. Zooming in shows street names, lots, and buildings. Clicking on a colored footprint opens a pop-up window with images and data.
The 249 buildings outlined on our map represent a span of years from 1874 through 1900. To accurately place the building footprints, including the 115 that have been demolished, we needed a historic map from 1900 or after. The best version available to us was the 1909 edition of the G. W. Bromley and Co. Atlas of The City of New York; the version we purchased was updated in 1913, 1914, and May 1915.
The 1909 Bromley is a Manhattan “land book” published in five folio-sized volumes of individual plates measuring 30 x 20 inches. These highly detailed plates identify streets, addresses, and, often, building names; block and lot numbers; precise building dimensions and lot coverage; height in stories; street and sidewalk widths; and other geographic information. The Museum used 101 plates of the Bromley Atlas, which we stitched together into one continuous map. This process allowed us to create a map that is both draggable and zoomable – a format and function that to our knowledge exists nowhere else in a map of this period with this level of detail.
To create an interactive and zoomable map we needed to make a modern base of the contemporary street grid with digital coordinates to serve as an anchor for our historic map with the colored building footprints. Ultimately, we geo-referenced and geo-coded all the footprints on the Bromley so that the historic map could be enlarged to show a high level of detail, including building measurements. This daunting process entailed around 1,500 hours of work!
Using the data set created by structural engineer Don Friedman from his study “Structure in Skyscrapers: History and Preservation,” the Museum staff and interns identified each of the 249 building footprints and outlined them in Photoshop on the individual plates of the 1909/1915 map. Because no one map provides a detailed portrait of our time frame, to correctly outline the footprints of buildings that had been demolished or modified by 1915 we had to reference older maps. A few footprints therefore are drawn over only a portion of the later building site.
In order to create the one continuous map, we “cut out” the individual plates from their pages in Photoshop, removing the borders. Once the separate plates were ready to be added to the map we had to geo-reference them using Arc Map GIS software. Geo-referencing is a process of assigning real geographical coordinates to a raster image, like the scan of a historic map. To do this, we went through every plate and linked blocks and corners on the 1915 map to where they would have existed on our modern map. We made sure to keep the true street grid from 1915, so certain avenues that were widened or streets will purposely not line up with the modern map. This time-consuming process gave us an accurate, comprehensive map of Manhattan circa 1915.
The building footprints, recreated as vector objects, were then overlaid as their own layer on the historical and modern map. We linked each footprint to a database that sorts the individual buildings by type, location, and year-built.