If you take a look at old photographs of any city, you’ll see a great deal of difference between what the geography used to be and what it is now. Buildings go up and come down, housing tracts are formed, cemeteries are plotted. WIth enough pictures, you can track an entire city’s history…but it would be relentlessly time consuming.

Google Earth is hoping to change all that with their partnership with the David Rumsey Map Collection, an online archive of historical maps and cartographic material. Rumsey’s archive includes maps made by aerial photographer Harrison Ryker, who, in 1938, commissioned pilots from Oakland Airport to create innovative images of San Francisco. The high-resolution photographs were taken in twelve aerial sweeps, creating 164 images to merge into a single large black-and-white print of the city.

The fascinating orignal photos can be seen at the San Francisco Public Library, but now people around the world can enjoy them–and overlay them with newer photos of the city–with Google Earth. By clicking on “historical imagery” within Google Earth, viewers can see the 1938 photos merged with current satellite photos, lending an entirely new–if somewhat ghostly–way to see the history of the city.

“These photographs combine the best aspects of photographic veracity and immediacy with the scale, artistry, and cartographic tools of mapping. It is like combining a photograph and a map of the same place, together,” David Rumsey said.

His hope is to find more photos like these of other cities to try and flesh out their histories, as well. The United States have such a varied, long memory that it may be difficult to locate such well-preserved artifacts; however, Google Earth can help to fill in the gaps in these mosaics for a lifetime of future cartographers.