Some dates are listed twice under the "select a date" drop-down menu, indicating one atlas held by the Census Bureau and one by the Library of Congress. Census Bureau maps are indicated by an asterisk (*). Corrections between editions were pasted onto these maps and not on maps held by the Library of Congress, so they are not identical. A map edition that shows a brief range of years means that the maps took that period of time to produce. Maps with longer ranges indicate pasted-on corrections were made to that map over that period of time from when it was first produced.
For large cities, maps are divided into multiple volumes for a particular publication year. If a year's edition had to be broken up into volumes, a new drop-down menu will appear at the top of the thumbnail page. Volumes are organized geographically, so consult the index map at the beginning of each volume to note what portions of a city are represented by what volume. On each index map you will find another map, called an insert map, in one corner with the city divided into several sections. The numbers in each section designate in which volume you can find your desired area.
At any time, you can change the city, date, or volume number of the Sanborn Maps displayed by clicking on the drop-down menus at the top of the thumbnail page.
Help with the page and collection is also available at the header present on all pages of the web collection.
Editors Notes, taken from the Library of Congress' published index of Sanborn Maps in its collection, appear in a pop-up window if you click on the "Editor Notes" link at the top of the page. Usually these notes indicate when nearby towns or suburbs have been included in a Sanborn edition.
Every time a thumbnail is clicked, a new window opens, displaying that map sheet instead of reloading a single window.
The Sanborn Maps are available both online and in microfilm in black and white, and the original maps in the Library are in color. The color maps give greater detail about the structures, while the black and white versions are less descriptive. To decipher the maps, utilize the following resources.
The Library of Congress has been digitizing Sanborn Fire Insurance Maps in color and has made them available at the Geography and Map Reading Room website. Not all of the maps are available at this time but many of the earlier maps are online.