For the first half century of fire insurance mapping, the dating
of editions is generally straightforward. For small-town maps issued
in loose-leaf format, the first page and generally each subsequent
page carried the month and year of publication quite prominently
in an upper corner of the map. The year of publication was usually
repeated as part of the copyright notice that appeared as part
of or adjacent to the title.
The dating of multi-volume editions of large-city maps is somewhat
more complicated. The date on the first volume may be valid only
for that particular volume, as the subsequent volumes may have
been issued over a period of years. In several cases, a single
volume within a multi-volume set was revised and reissued with
a new date even before the whole edition was completed. In Fire
Insurance Maps in the Library of Congress, therefore, date
ranges are given for the coverage of multi-volume editions.
Beginning around 1920, the dating of an edition becomes rather
complicated. In response to various economic factors around that
time, the Sanborn Map Company began updating maps for its customers
by issuing paste-on correction slips. These were generally applied
by a company employee, who then annotated a chart, usually entitled "Correction
Record," attached to the title page, recording the dates on
which corrections had been applied. Such correction slips were
intended to keep the map coverages current. Over the years, however,
more and more correction slips were added, and it is impossible
to determine which correction slips were applied in which years.
For many cities, as many as fifty or sixty series of correction
slips were applied over the course of thirty or forty years. In Fire
Insurance Maps in the Library of Congress, the dates for such
editions are the date of the original printed edition of the map
and the latest date for which corrections were applied.
The latest date, however, is not always found in the "Correction
Record." In many cases, additions to indexes pasted into an
atlas are later than the last correction slip annotation indicates.
In Fire Insurance Maps in the Library of Congress, the
latest date of an edition or volume reflects the latest date found
on any material pasted into that volume or edition.
The vast majority of examples of paste-on correction sheets in
the collections of the Library of Congress come from the maps produced
by the Sanborn Map Company from the late 1920s. This technique,
however, appeared very early in the history of fire insurance mapping.
When significant changes took place in a city, it was important
to update the fire insurance plans. In some cases, the amount of
change did not warrant mapping the entire city again. In other
cases, it may have been prudent to update certain key changes even
before the whole city could be re-mapped. To accomplish this, fire
insurance map producers printed a correction sheet that was pasted
over the incorrect information. Charles
Rascher, for example, in his 1891 atlas of Chicago, includes seven different
updates printed on a single sheet. Where a map producer had inventory
in stock, the corrections could be applied before the volume was
sold. At least some companies offered the service of sending employees
to customers' offices, where the correction sheets could be applied
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