In the last week since releasing the prototype of Pastmapper, I’ve been blown away by the level of interest. From all over Twitter, and from readers of Burrito Justice, Curbed SF, Huffington Post, EngadgetLa Vanguardia, and Design Boom, among others, the interest I’ve received has made it clear that there’s a lot of potential for Pastmapper.  I look forward to further discussions about how to move the Pastmapper project forward, and begin mapping more cities around the world and back in time.

A number of people have asked about how to help with the process, and I am thrilled about getting help. Eventually, I will create a formal set of requests and specifications, but for now, I’ll outline the basic steps for getting a map into Pastmapper. Today I’m covering Part 1:

Part 1 – Vectorizing The Map

The first step is the most important – creating a vectorized version of a historical map. This involves tracing contours and landmarks into lines that can be understood by graphics software, which can then be manipulated to create multiple zoom levels, color coding, and all of the features we have come to expect from online maps like Google Maps.

But vectorization is slightly more complicated than simply scanning a map and drawing lines on top. Before the lines can be traced, the maps must be georectified, or warped to align with current-day Google Maps, removing any discrepancies between differing map projections or other distortions that would cause roads, coastlines, and other features to be rendered inconsistently on an online map. Learn more about the process of georectification in this great post by Matt Knutzen at the New York Public Library.

From NYPL's Map Warper project

A warped map of lower Manhattan (image from the NYPL Map Warper project)

Luckily, thousands of maps have already been georectified — there’s a good chance that your city’s map has already been prepared for vectorization. Look for georectified maps at the NYPL Map Warper site, or check out David Rumsey’s GeoGarage, where you can browse to find the old maps available for your city. You’ll see, for instance, that 1852 New York is ready to be traced, as is 1831 Madrid, 1858 Tokyo (Edo, or 江戸), 1880 Los Angeles, plus dozens of others. I live in San Francisco, so I’m particularly excited about the 1915 ‘Chevalier’ San Francisco map.

1915 Chevalier Map of San Francisco

1915 Chevalier Map of San Francisco

Tokyo (Edo, or 江戸), 1858

Tokyo (Edo, or 江戸), 1858

Madrid, 1831

Madrid, 1831

For 1853 San Francisco, my base map was the 1853 US Coast Survey map. The image below show what it looks like in Illustrator to trace coastline contours, one line endpoint at a time.

Tracing lines

Tracing the northeastern San Francisco coastline of 1853

Eventually, Pastmapper will automate as much of this process as possible using browser-based tools, but in the meantime, a standard offline graphics program like Illustrator appears to be the best way to create these lines. If there are browser-based (and crowd-source-able) alternatives that you know of, please contact me; we should chat.

If this has piqued your interest, and you’d like to help, please get in touch with me. Let’s build Pastmapper together –  this has potential to be really interesting.

(Also, if you’re graphically-inclined, here is the task list, in nitty-gritty detail, outlining my current vectorization process.)

Coming soon, the next steps:

Part 2 – Drawing and Populating the Map

Part 3 – Adding Data (People, Buildings, Photos, Videos)


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  1. […] broaden the scope of the project, Thompson is looking for help from volunteers who can help create historical layers by vectorizing georeferenced historical maps.  The process […]