Pastmapper is a new platform for organizing data using the visual language of online maps to describe the world of the past. It’s also the manifestation of months that I’ve spent tracing old maps in Illustrator, learning to hack together code with the Google Maps API, and cramming 19th century city listings into a database.

For quick access to realtime information, (photographs, Tweets, business listings, weather, voting results, etc.), online maps are incredibly powerful tools. The more realtime the information is, the more valuable it is, and maps are in a constant state of being updated to keep up with the world. These tools are generally suited for answering a question that begins ‘What is happening?” or “What just happened?”. A few amazing examples of current data on maps are Eric Fischer’s racial distribution maps, the Oakland Crimespotting map by Stamen Design and the New York Times Hurricane Tracker.

But what if your real interest is what happened further back in the past? Online maps today simply add layers of information onto today’s map. Pastmapper is a first step towards answering ‘What was here?’ or ‘Whatever happened to..?’, by delivering a map, not just a data layer, that takes a fourth-dimensional view.

Version 0.1

What I’m sharing today is just a prototype: a working example of the Pastmapper experience that I hope to scale to every location and every year (this is no small undertaking!) This prototype presents San Francisco as it was in 1853, using geometries from a scan of the US Coast Survey Map from the David Rumsey Historical Map Collection. A lot has changed in the last 158 years. Hills have been leveled, coastlines have expanded, and points of interest have been renamed. A staggering number of streets have been closed, opened, renamed, or widened. Building numbering in San Francisco changed completely in 1861, so even the street addresses don’t match their 2011 counterparts.

San Francisco 1853 map

But Pastmapper is more than simply redrawn maps. In this prototype, city directory information from the September 1852 A.W. Morgan & Company’s San Francisco City Directory is overlaid, but this a small glimpse of the old data that can make the past more accessible and relevant. There is an opportunity to apply the full richness of the Google Maps experience to the depths of history.

What Comes Next

Today’s release represents a very small part of Pastmapper’s potential. Imagine being able to look back in time at your neighborhood, to see how businesses and landmarks developed. Your local cafe might have been a saloon, or a speakeasy, or a soda fountain – or all three, at different points in time.

Pastmapper will let you explore the complexity of the past, to dig deep into stories from different time periods all over the world. When would you like to explore? America before interstate highways? Chicago’s speakeasies during Prohibition? Europe before the urban wreckage of World War II?

If you have feedback, suggestions, or would like to help, please drop me a line and follow me on Twitter. This is just the first step.

Tagged with:
16 Comments » for What is Pastmapper?
  1. Stuart says:

    Looks great! A great tool to see change over time.

  2. Philip Ferrato says:

    We did a quick post on Pastmapper today at Curbed SF:

    Congratulations. It’s brilliant.

  3. I am skeptical about the 1853 addresses matching up to the 2011 locations. What method do you use to verify these? For instance, on the 1853 map there seem to be very few buildings on the south side of Clay between Montgomery and Sansome, but there are a lot of dots and a lot of different addresses. Also, zooming in to the map seems to be disabled, so it’s hard to select individual markers. Otherwise, it looks great congratulations on all the hard work.

    • Pastmapper Admin (Brad) says:

      Hi David –

      Thanks for the comments! I’m glad to see you found the site. You raise some good points, and I think I can address them adequately:

      Address Matching
      First, you’re right that 1853 addresses do not match any 2011 counterparts; this has made the geocoding pretty laborious. First of all, the numbering scheme currently used, wherein each block contains addresses within a range of 100 numbers (hence, the 200 block, 300 block, etc) wasn’t implemented until 1861. Because of this, I couldn’t use today’s Google Maps database to determine the latitudes and longitudes. Instead, I had to devise the geocoding myself. My method involves assigning latitude and longitude values to the minimum and maximum extents of each side of a street, for each block, (manually) and entering these into a spreadsheet. Then I take the corresponding minimum and maximum street numbers from (the a contemporary account of the city). Once I have these ranges established, I calculate the relative position that an individual listing would have between the block’s minimum and maximum street numbers. For example, addresses on California Street between Leidesdorff and Montgomery ranged between 121 and 140, so I make an assumption that 133 California Street was 63% down the block, on the left (south) side of the street. I take that 63% value and extrapolate a corresponding latitude and longitude. This assumption assume an even distribution of address numbers, which is probably not exactly right, but as far as I can tell, it’s the best guess available for most of these listings.

      So far, I’ve only geotagged 26% of the directory; you can expect to see that number increase soon.

      The buildings shown on the map, taken from the Coast Survey, haven’t all been included on Pastmapper. You’ve got a good eye – thank you for noticing! All of the buildings outside of the developed part of the city are complete (Hayes Valley, Mission Dolores, Washerwoman’s Lagoon, etc), but the built-up areas are incomplete. The process of vectorizing these building outlines takes awhile too. I won’t go into it in detail here, but you can expect to see these fill in over the next couple of weeks.

      Additional zoom levels are at the top of my to-do list – you’re exactly right that zooming will allow a better experience. Each zoom level has to be drawn individually, so for the time being, zoom level 16 is the only one that’s finished. Look out for zoom level 15 soon; that’ll let you take a closer look at the listings and the buildings.

      Thanks for the interest! I look forward to sharing these updates soon.

  4. Juancho says:

    Excellent explanation and tools!:)

  5. Eric says:

    What a fantastic project! Sounds like a lot of work. Is there a way we can help?

    • Pastmapper Admin (Brad) says:

      Hi Eric – thanks! And yes – I would love some help. I’ve written a blog post about the vectorization process ( and I’m working on the next one, in which I’ll explain how people can help by providing structured data. If you’d like to chat more about how to help, or would like to work on a particular place or era, drop me a line at and we can chat. Cheers!

  6. The Pastmapper project is beautiful, the more history the better. We are “mapping” the history of our street, from 1880 until today, facing some of the same problems.
    Have a look at

  7. Stefan says:

    Amazing stuff! Will follow the progress of this endeavor with great interest.

  8. Looks really good. Excellent project! Hopefully you get some interest via Ireland:

  9. AdamP says:

    What a great Idea. I am wondering if there is a way to crowd source this activity. Perhaps define a standard data model and have volunteers from different areas build their cities. I am sure that you could leverage this to escalate the timeframe. You could even establish a wiki editing model were historians could update maps based on their research. They could even geo-tag historic photos and add them to the locations.

  10. Brian says:

    I love your idea !! You sure got a FULL plate !
    If it’s half as good as your explanations ,you will be successful.
    Sorry,I don’t know enough computer tech to be of much help.
    I can’t wait to apply it to metal detecting, hobby & finding those truly OLD sites with my father &finding kids.
    Best of Luck on your lofty project.

  11. Andrew says:

    We have essentially done this for the City of Chicago. We call it “The History Map,” and you can find it here: If you click the category icons, you will remove them from the map, just as they are doing with Pastmapper. In addition, clicking on the map retrieves a pop-up box (as here), except that you can follow the links in our pop-ups for additional information. Three cheers for Pastmapper. We love this concept and believe that the future lies in the dissemination of location-based content.

  12. Alberto says:

    Spectacular! I want this a good idea to be developed for all major cities worldwide. I’m from Buenos Aires – Argentina and I would like to see my city using the old time. I study the history of my city and its old buildings. Keep up this project, many people will use it because it is very interesting. Luck and Best Regards.

  13. Pat Dugan says:

    What a fantastic idea. I am particularly interested in the area around the current Duboce Park Neighborhood. My great grandfather built a house acroos the street from the Park. My granpa told stories about a creek that ran on the north side of the Park that he would play in as a kid.

6 Pings/Trackbacks for "What is Pastmapper?"
  1. […] atrás para saber cómo eran entonces las ciudades. El milagro que lo permite lleva el nombre de Pastmapper, una plataforma que utiliza el lenguaje visual de los mapas online para describir el mundo en el […]

  2. […] – Blog de Brad Thompson sobre Pastmapper. […]

  3. […] nueva plataforma permite a los usuarios viajar al pasado a través de Google Maps. Pastmapper traslada a los usuarios varios siglos atrás para saber cómo eran entonces las ciudades. Esta […]

  4. […] a scan of the US Coast Survey Map from the David Rumsey Historical Map Collection.  Thompson explains:A lot has changed in the last 158 years. Hills have been leveled, coastlines have expanded, and […]

  5. […] ha volgut superar-se a si mateix. I ara Google Maps ofereix la possibilitat de viatjar al passat. Pastmapper és una plataforma que utilitza el llenguatge visual dels mapes on-line per descobrir el món com […]

  6. […] We’re going to start it off with a short review of which describes itself as “a new platform for describing the world of the past“. […]