The maps were published in atlases with a decorative title page, usually with impressive typography, like this 1920 cover page from Portsmouth, NH (below). The maps were at a scale of 50 feet to an inch, allowing for detailed outlines of buildings and outbuildings, property boundaries, street names and addresses, descriptions of building uses, and naturally, locations of fire hydrants and fire departments. The atlases also featured indices of streets, public buildings including schools and churches, and information about the population and economy.
The Sanborn maps are useful to all kinds of people. For historical archaeologists, they are a great resource for viewing neighborhood change over time. In the image below, I've collected portions of the Portsmouth maps from 1878 through 1941 which show the neighborhood block where we'll be digging this summer. The house at 90 Jefferson Street appears in the center of the block on the 1904 map, replacing Augustus K. Brown's barn. As you can see in the maps, buildings (especially outbuildings) came and went over time. Today, only the Marden-Abbot house (in the NW corner) and the Lowd House (in the SE corner) still stand. It is interesting to correlate these maps to historic deed descriptions and directories. This summer, we will also get the chance to ground truth the barn foundation and property line.
Below is a portion of the 1910 Sanborn map georeferenced over recent aerial imagery of Strawbery Banke Museum. In this type of overlay it is clear that there have been many changes to the landscape of the Puddle Dock neighborhood in the last century.
Interested in searching for a historic Sanborn map of your neighborhood?
The Library of Congress has a collection of Sanborn maps searchable and available online.
Many NH Sanborn maps are available online at the Dartmouth College Library.
David Rumsey's excellent Map Collection has scans of a rare 1905 San Francisco Sanborn Atlas, which shows how the atlases were arranged.
The New York Public Library has been engaged in a very cool NEH funded project to scan and georeference nearly 8,000 Sanborn maps of NY and NJ.
There is also a searchable database of PA Sanborn maps and a lot more information on the Penn State University Libraries website.