Interpreting Sanborn Indexes
Graphic Index (or Key Map)
For researchers, an important part of the prefatory material is
the graphic index that portrays the areas of the city covered by
each sheet in the edition. In the case of multi-volume editions,
there is often a "Graphic Map of Volumes" that shows
the portions of the city covered by each volume.
The graphic index is frequently referred to as a "key map." When
a researcher wishes to examine the coverage for a portion of a
city, the graphic index is more useful than the street or other
indexes. Key maps serve two purposes: they show the areas encompassed
by individual sheets and indicate the portions of a city or town
that were mapped. Coloring was generally used on key maps to indicate
the area covered by an individual sheet in the edition or atlas.
There are usually compas roses, often highly decorative, to orient
the user, but not always scales.
Street Indexes
A street index from a small town |
One important component of a fire insurance map or atlas is the
street index. In theory, street indexes are rather simple. Street
names are listed alphabetically, including numbered streets and
avenues, which are spelled out in full. Subheadings under the name
of a street frequently indicate address ranges covered by individual
sheets in the edition or volume. For some large editions and atlases,
however, this index may also contain a separate listing for a special
component of the city, such as wharves and piers. In using these
indexes, it must be remembered that street names and building numbering
systems could change several times in a given city during the century
and a half in which these maps were prepared. Trying to find the
historical equivalent of a current address can be rather difficult
if researchers try to rely strictly on the street indexes. In many
cases, it will be necessary to relate an address on a current map
to the key map described in the previous section. On the other
hand, when working only with a written record of an address, street
indexes are essential for locating buildings for which the street
or number has changed.
Special Indexes
Example of a Special Index |
An interesting look at the life of a city can be found in an index
of specific properties that sometimes appears separately but may
also be a continuation of the street index. The name of this index
usually includes the word "Specials." It identified major
businesses, public buildings, factories, or other large structures.
Such indexes were prepared to facilitate quick location of these
major features. For current researchers, however, the list of "specials" is
the equivalent of an abridged city directory that provides insight
into the economic and social landscape of a community. From one
edition of a city to another, entries in these indexes will come
and go, and a particular business or institution will change its
name to reflect new owners, a new function, or a modernized sense
of propriety.
How to interpret:
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