If you wanted to make a map of your town before Google Maps, satellite imaging, planes, or even cars existed, you had to walk there and chart the landscape by hand.
Now, all that decades-old topological hard work is available online thanks to a United States Geological Survey (USGS) project to digitize over 200,000 old topographic maps of the United States. The USGS Historical Topographic Map Collection is a free, searchable online portal to historic maps that were previously only accessible by physically going to the USGS archives in Virginia.
The project originally began in 2009 to preserve and improve public access to the maps. The USGS has already digitized its entire collection of maps of the continental United States and Hawaii. It also plans on releasing its remaining maps of Alaska, Puerto Rico, the Virgin Islands, and the Trust Territories by September of this year.
The online map archive includes San Francisco from 1947, Chicago in 1929, and Utah in 1885. Why only so far back That's because Congress created the USGS in 1879 to locate potential mineral deposits.
It's a great resource if you want to check out what the American landscape used to look like when New York was part swampland, or how the Mississippi River used to run before we started messing with it.
[USGS Historical Topographic Map Collection via Smithsonian Blog and The Verge]