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A tool used by historians to trace the history of a city is a special map, called a Sanborn Insurance Map. The maps were published for insurance agents to assess the risks of insuring a particular piece of property and were first published in 1867.  

Sanborn Maps are filled with information. They are large-scale maps drawn 50 feet to an inch. A Sanborn map is printed on heavy rag paper and bound in huge books that are about 2x3 feet. Each page contains about 4 or 5 blocks.  

If a city is large, the map is divided between several volumes. Berkeley, for example, is now divided into four volumes and each volume contains about 100 pages. The earliest Sanborn map of Berkeley dates from 1894 and was only one volume with 14 pages. It only covers the blocks around the downtown train station, the area south of the university and along Shattuck to Rose Street. The other areas of Berkeley were so sparsely populated that there was no need to map it. By 1911 Berkeley had grown so large that the map was revised and divided into two volumes. The next revision occurred in 1929 and was divided into 3 volumes.  

The most important aspect of Sanborn Maps for a historian is that they show the outline of properties and the footprints of buildings and these are fairly accurate. Addresses are also shown. The footprints of structures show porches, turrets and window bays providing clues to the age of a building.  

The maps were color-coded and had symbols for different types of structures. If a building is wood-framed it is indicated in yellow, brick in red. A windmill and water pump is indicated by a circle within a square, and a stable has an "x" through it. If a building was a dwelling it would be indicated by a "D". Fire hydrants and water pipes, including their size, were shown.  

The maps were kept up-to-date by the Sanborn Company who provided changes that their customers (insurance agents and city planning departments) could paste into their maps. When changes and annexations had become extensive, the company issued a new map. By using different editions of these maps the historian can see how an entire city or particular piece of property changed over time.  

The latest Sanborn Map for Berkeley can be viewed at the Building Permit Department on Milvia Street. Older ones are available on-line. 

Susan Cerny is author of Berkeley Landmarks and writes this in conjunction with the Berkeley Architectural Heritage Association.