From the post:
Geospatial data lovers know that proximity has its perks- especially in a major city like New York. We recently spent a few minutes browsing through the work of New York Public Library’s Map Division and discovering all of the awesome tools they’re creating- one of which we are about to share with you. World, meet (or re-meet for those of you who already know) MapWarper: The NYPL’s open-access tool for rectifying historical maps from its collections and making them available to the public.
The library’s developer team has been seriously cranking, so you have almost 10,000 maps to peruse and use. How in the what, you ask? Gain behind-the-scenes insight on MapWarper magic from the above video and this blog post, both courtesy of the NYPL. In addition, support the cause by aligning cool maps you come across during your searches that are in need of special attention. MapWarper makes it easy for you to DIY rectify with a built-in “Edit” function.
Source: Resource: Using NYPL MapWarper maps inside CartoDB — CartoDB Blog