Where there’s smoke, there’s fire insurance maps

Prior to this week, I had never cataloged maps or atlases. My favorite thing about being a cataloger is learning new things — unfamiliar subject matter, but also how resources differ, and why those differences matter. Cartographic materials contrast greatly with the books and periodicals I normally encounter on the job. As a child, I was fascinated with maps and plans; sometimes I would draw maps of imaginary places, or cross-sections of fantastic buildings and caves. As an adult, however, I did not pursue cartography, geography, architecture, or any of the other professions that involve graphical representations of our natural and built environments. As a cataloger, I work with symbolic representations of primarily textual materials, so I faced a learning curve in cataloging Sanborn maps.

The Library of Congress maintains the world’s largest Sanborn Map Collection, which includes “some fifty thousand editions of fire insurance maps comprising an estimated seven hundred thousand individual sheets.” I recommend you read the linked essay, which is more interesting than I expected it to be, and provides a depth of context that’s not possible here, even if I knew the topic well.

Insurance maps of Des Moines, Iowa. New York: Sanborn Map Company, c1920.

Insurance maps of Des Moines, Iowa. New York: Sanborn Map Company, c1920. (Gift of Jerry J. Jennett, June 2016.)

One day I was hard at work, minding my own business, when along came three big books. You could have heard a pin drop: these bad boys are just over two feet square, and heavy. I ended up describing them as “1 atlas in 3 loose-leaf volumes (ca. 310 sheets).” In other words, it’s a huge map of Des Moines divided into a grid on about 310 sheets. If you’ve used road maps, then you know the basic format — once the map is too big to fold, it gets broken up. Breaking up these maps introduces the need for indices and “key maps,” without which the user would be lost.



V. 1 KEY MAP (DETAIL). Insurance maps of Des Moines, Iowa. New York: Sanborn Map Company, c1920.

Above you see a small portion of the key map (scale: 1:12,000). Each numbered shape corresponds to one of about 310 “sheets” (scale: 1:600 or sometimes 1:1,200). As we’ll see further on, the 1:600 scale sheets are rich in details that the fire insurance companies valued.

Confusingly, Sanborn “sheets” are printed on both sides of the leaves (at least in this format). It’s tempting to think of these “sheets” as the pages of a folio, but the similarities are superficial. The distinction is a subtle one that I have struggled to describe. Documents have different structures; consulting a reference work is very different from reading a linear, unidirectional text. The Sanborn atlases are graphical reference works for a very particular audience. Numbered sequences — whether of pages, leaves, or other elements — are a feature of resource types that are in other ways dissimilar. Looking at our three-volume map of Des Moines, I can see why some owners would choose to disassemble it (or not acquire the whole set). It’s not surprising that the Library of Congress collection includes a great many “sheet maps” that are not bound into loose-leaf volumes like ours.


A TYPICAL SHEET (DETAIL). Insurance maps of Des Moines. New York: Sanborn Map Company, c1920.

Here we have a city block represented in a specialized manner. Notable are (1) the nature of the details, and (2) the evidence of revision.

(1) Annotations like “fire proof construction” and “paints & oils” were obviously of interest to the fire insurance companies that bought these maps. What is not clear from this closeup is that the buildings are color-coded: a brick building is shown in pink, a stone building in blue, etc. The insurance companies were also very interested in doors, windows, elevators, and certain other features; you’d need the key to understand the relevant symbols. Not shown above: notes on building security. Important buildings had one or more night watchmen who were noted on the map. Regular patrols might be tracked with watchclocks; “approved clock” is a favorable map note, “no clock” is a bad one indicating that the watchman could muck up his route or skip patrols altogether.

(2) Look closely — see where littler pieces of paper were pasted over the original sheets? These maps were originally issued in 1920, but they were revised many times. Sanborn employees would revise your maps and note the changes in a log. Sometimes they removed whole sheets and replaced them with new ones. An index might get an addendum, or it might be completely pasted over with a new one. The big changes are not mysterious — they are labelled or logged. The little changes are impossible to nail down. Did a Sanborn representative do them?… All I know is that our copies were altered at least twice a year, 1934 through 1937. The sheer number of little paste-overs is mind-boggling!

You can see these books at Special Collections and University Archives, ISU Library. Here they are in the online catalog. 



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