There are two legends you can use with the maps: the original key and a black and white key, which was developed specifically for use with black and white copies of Sanborn maps. Color on the original Sanborn maps indicates building material, such as stone or wood. The black and white key lists markings on the maps that indicate building material. The earlier versions of Sanborn maps do not include these markings and rely solely on color to list building material. Symbols not indicating building material are the same on both legends.
Note: Because the key is a detailed file, it must be large so that you can view it completed. As a result, it may take a while for the key to display on your screen.