Cartographic Rectification

A recent post at the Fresh Kills Park Blog showed the beauty and function of the process of map rectification in GIS, where a map and image can be combined by matching ground control points in the mapping system to points in the image. As it may be well known, I'm constantly fascinated by historic maps as a tool for understanding and creating modern moves in cities, and recently I expressed a desire to do this with a series of Portland maps.


:: image via Fresh Kills Park Blog

These maps aren't 100% accurate, as they rely on consistent base points to align common map features, and often lack in accuracy - but do provide a great overview of layers of history. An indication of the product is shown on the FKP site - a rectified map of the landfill site (above): "A 1907 map of the Fresh Kills area helped us understand a little more clearly the extent of filling in creeks and wetlands, and also the sense of private ownership that this land did, in fact, enjoy prior to the start of landfill operations–the entire site was entirely carved up into privately owned parcels."

In this case, it isn't a particularly unattainable venture, thanks to the New York Public Library beta version of their map rectifying tool (aka Warper) online: "...that allows users to digitally align or “rectify” historical maps from the NYPL collection with today’s maps and aerial photos. You can browse previously rectified maps or sign-up for an account to align your own and add it to the browse-able archive"

Check out a short video of the tool:


These processes bring to mind of course the wonderful Mannahatta Project by Eric Sanderson, which used rectified historical maps to provide a . I just finished devouring the book, so look for a post soon.