How to Use and Understand Maps: How-To

Consult our LC Map Call Numbers Finding Aid, an alphabetical list of countries, regions, states, and cities with an emphasis on the Pacific Northwest.

Library of Congress call numbers for maps can be broken down into several basic components:

• where,
• what,
• when,
• which scale, and
• who created it.

(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:

• 0 or 5—a general map of the geographic area
• 1 or 6—map of a subject within that area (roads, geology, etc.)
• 2 or 7—map of a region or natural feature (body of water, mountains, island, etc.)
• 3 or 8—map of a major political division (county, state, province, etc.)
• 4 or 9—map of a city or town

So, for example, if G4280 is the general call number for Washington State,

• G4281 indicates that the map is about a subject within the state of Washington (ex. mineral resources)
• G4282 indicates that the map is about a region or natural feature within Washington (ex. Mount Rainier)
• G4283 indicates that the map is about a major political division (ex. King County)
• G4284 indicates that the map is about a city or town (ex. Issaquah)

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.

Examples:

• A general map of WA state has the following call number:
  G4280 1987 .A4
  where (G4280—WA state), when (1987), who (.A4—Allen Cartography)
   
• A map of the roads of Seattle has the following call number:
  G4284.S4P2 1999 .T5
  where (G4284—WA state by city; .S4—Seattle), what (P2—roads), when (1999), who (.T5—Thomas Bros. Maps)
   
• A topographic map of India has the following call number:
  G7650 s250 .I5
  where (G7650—India), which scale (s250—1:250,000), who (.I5—the Indian government)

The United States Geological Survey (USGS) has a detailed description of topographic map symbols.