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Maps Research Guide

A compilation of print and online resources on how to locate and use maps.

Map Call Number Overview

This page contains information on the different map call numbering systems, including Library of Congress and SuDoc, that are used on maps in the Mansfield Library and Archives and Special Collections. To locate specific maps held in our collections, you not only need to know the location of the map (Level 1 or Level 4), but also the call number of those maps. Map call numbers may be found by searching the library's online catalog, OneSearch.

If you don't know the call number for a map you'd like to find, ask for assistance at the Level 3 Reference Desk or the Montana Room Reference Desk.

How to Read Library of Congress Call Numbers

The Library of Congress Classification (LCC) is a classification system that was first developed in the late nineteenth and early twentieth centuries to organize and arrange the book collections of the Library of Congress. Over the course of the twentieth century, the system was adopted for use by other libraries as well, especially large academic libraries in the United States. It is currently one of the most widely used library classification systems in the world.

The system divides all knowledge into 21 basic subject classes, each identified by a single letter of the alphabet. Most of these alphabetical classes are further divided into more specific subclasses, identified by two-letter, or occasionally three-letter, combinations.

LCC 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.

  • Maps with the G 4250 through 4254 are maps of Montana.
  • Maps with the G 3701 call number stem are U.S. historical maps. This includes U.S. territories before they became states and Indian reservations.

What is indicates the subject matter of the map.

Each geographic area can be additionally broken down by subdivisions, based on the last digit. For example, if G4250 is the general call number for Montana State:

  • G4251 indicates that the map is about a subject within the state of Montana (ex. mineral resources).
  • G4252 indicates that the map is about a region or natural feature within the State of Montana (ex. Flathead Lake).
  • G4253 indicates that the map is about a major political division (ex. Ravalli County).
  • G4254 indicates that the map is about a city or town (ex. Missoula).

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, such as .U5. This is called a Cutter number or a Cutter.

source: Library of Congress Classification

How to Read SuDoc Call Numbers

The SuDoc classification system stands for Superintendent of Documents. It was created and is maintained by the U.S. Government Publishing Office (GPO). Only maps produced by U.S. government departments may be cataloged with a SuDoc call number.

Each SuDoc call number begins with the initial of the particular government department that created the map. (For a complete index, see Appendix I.)

What does “SuDoc” mean? 

 “SuDoc” or “SuDocs” is short for “Superintendent of Documents.” The Superintendent of Documents is in charge of the Federal Depository Library Program (FDLP), the program that sends copies of government publications to libraries all over the United States and its territories. The SuDoc classification system is used to organize publications issued by the federal government.  

There are three main things to know about SuDoc numbers.

1. Organized by agency

The SuDoc system is a “provenance-based” system, meaning that documents are organized by the agency that issues them (where they come from). So, all the Forest Service documents are together on the shelf, all Defense Department publications are together, and so on.

The first letter of the SuDoc call number, or class stem, indicates the parent department. For example:


Department of Agriculture   S State Department
C Department of Commerce   SI Smithsonian
I Department of Interior   Y Congress


The next number in a SuDoc call number indicates the sub-agency that produced the publication. Using three Department of Interior agencies for example:

I 19

U.S. Geological Survey
I 20 Bureau of Indian Affairs
I 29 National Park Service


For a complete list of SuDoc class stems and the department with which they correspond, visit the SuDoc Classification Scheme webpage.

2. Whole numbers, not decimal numbers

Unlike the Dewey Decimal System, numbers in a SuDoc call number are whole numbers, not decimal numbers.Comparing the same set of numbers in the two systems you can see the difference in shelving:

Dewey Decimal Order

SuDocs Order
D 1.1 D 1.1:
D 1.12: D 1.3:
D 1.122: D 1.12:
D 1.3: D 1.33:
D 1.33: D 1.122:


3. One document, one number 

SuDoc numbers are typically assigned by a central organization, the Government Printing Office. Each document gets a unique call number, and that number should work at any other depository library that uses the SuDoc system. Therefore, if you see a SuDoc call number in another library’s catalog, on WorldCat, or in a printed reference work, check our library’s shelves—if we have it, it should be at that number.

Where did this system come from?

The foundation of the system was created by Miss Adelaide R. Hasse, while she was assistant librarian in the Los Angeles Public Library. The system was further developed in the Library of the Government Printing Office between 1895 and 1903. The system has been in use for over 100 years now and is used by most depository libraries for their government documents collections. The National Archives also uses the system to organize their copies of government publications.  

 Want to learn more?

Try the Learning SuDocs Call Numbers interactive tutorial from the Michigan State University Libraries provides more in-depth information on the system and includes a quiz and virtual shelving exercises.

source: Mansfield Library Government Information Research Guide