Library of Congress call numbers for maps can be broken down into several basic components:
(Not every component is present in every call number.)
Where is represented by the letter G and four numbers. Consult our partial list of geographic areas for more information.
What—that is, the subject matter of the map—is a bit more complicated.
Each geographic area can be additionally broken down by subdivisions, based on the last digit:
So, for example, if G4280 is the general call number for Washington State,
A general map (ending in 0 or 5) will not have a subdivision. All other kinds of maps (ending in 1-4 or 6-9) will.
When—the date of publication—is represented by a year. If the year of publication is not known, it will have a question mark and may also have one or more dashes. For example, 197-? indicates that the cataloger believes that the map was published sometime in the 1970s.
Which scale is only used for sets of maps all in the same scale, such as topographic sets. It is represented by the letter s and a number. For example, s250 represents the scale of 1:250,000.
Who—the author of the map—is represented by a period, one letter, and one or more numbers. This is called a Cutter number or a Cutter.