Wednesday, January 13, 2016

Scratch and Sniff New York's History

Created by Chris Whong ("Urbanist, Mapmaker, Data Junkie") Urban Scratchoff allows you to  scratch your mouse along a 1924 aerial photo of New York City to reveal the present day aerial view.
Or you can flip the images and scratch the old from the new. In the picture above, I scratched a modern view of my grandmother's former Bronx apartment building (and adjacent buildings) into what was apparently some empty lots in 1924. Here is an attempt to reverse the process.
The wonky stuff: The scratching is done using HTML5 Canvas with a jsfiddle called Canvas Eraser. The 1924 map is from the New York Public Library, which has a mapwarper site that allows users to rectify historic map images so they fit over aerials. The images are tiled and displayed using Leaflet. The project is on Github, allowing others to add different historic images or replicate it in different cities. A much more thorough discussion of how this was done can be found on Whong's blog post.

Many of New York's neighborhoods show little change from 1924. The best places to see significant changes are around airports, stadiums (former and current), industrial sites and waterfronts.
Here is the former Polo Grounds scratched out from the current Housing Authority towers.
An example from DUMBO:
You can also scratch out secret messages:
I can't believe I just did that! I'm an awful person !

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