The Anatomy of a Call Number

I recently saw a public library Instagram reel that explained the breakdown of an entire call number of a book—using the Dewey Decimal System. The video pointed out that the demystification of these call number codes can be incredibly helpful to our users. If users can de-code the sequence, they can unlock how to find, store, and classify materials in a library—even maps in the cartographic collections at the Library of Congress! Users can then apply this knowledge when browsing the online catalog or when physically browsing the shelves to discover our holdings—using it like a guide to find similar material or like an address to locate objects in the stacks. The call number may also be referred to as a shelf number, which is just another way to indicate that the materials are shelved or stored in call number order in the stacks. This post aims to help users understand what call numbers are and how to use them to find maps and other cartographic objects in the Geography and Map Division.

To get started, the Geography and Map Division relies on Library of Congress Classification (LCC) to establish call numbers. LCC is a classification system that was first developed in the late 19th and early 20th centuries to organize and arrange book collections of the Library of Congress. Today it has expanded to maps and other materials, and is one of the most widely used classification systems in academic and research libraries worldwide. LCC uses twenty-one letters of the alphabet to indicate broad subject areas—this is the first letter in the call number. A simple example of a map call number is G3200 1811 .D3.

An important principle to keep in mind when dealing with LCC is that the classification reflects the geographical area or areas depicted in the resource—it captures what the map is about. The classification gets more complicated with two and three areas covered, so review the division’s Cartographic Resources Manual for those principles if interested in more complex classification.

Let’s break it down. We now know that LCC orders or arranges maps (and other materials) by geography and subject. A call number for cartographic material starts with a five-character alphanumeric code. The first character is always one capitalized letter—G—followed by four integers ranging from 1000–9999 with possible decimal extensions. We refer to this part of the sequence as the base classification or class number. The G stands for the broad subject of geography, and it is followed by a four-digit code that identifies the geography of the object. For example, the class number of the call number should look something like this G1019 or G9804. The class number of the call number is the element that we will focus on understanding in this post.

In general, cartographic formats have their own range—all atlases will fall between class numbers G1000–3122, globes between G3160–3171, and maps between G3180–9980.

Digits can be added to each class number to get more granular within the geographic area and with the subject matter. To illustrate this concept, we can look at Massachusetts. General maps of the state of Massachusetts are all classified together in chronological order under the class number G3760; subject maps of the entire state of Massachusetts are filed by subject, e.g., administrative, climate, demographic, geological, population density, roads, etc., under G3761; maps of regions, e.g., Cape Ann and Cape Cod National Seashore, are filed together under G3762; maps of counties, e.g., Berkshire and Middlesex, are filed together under G3763; followed by maps of cities or towns, e.g., Boston and Dalton, filed under G3764.

Class numbers for maps depicting Massachusetts:

•  General G3760
•  Subjects G3761
•  Regions G3762
•  Counties G3763
•  Cities and towns G3764

Most of the map collection call numbers include geographic cutters—there are also subject and author cutters. A cutter number is a method of representing words or names by using a decimal point followed first by a letter, then by one or more integers. It falls right after the class number. Geographic cutter numbers correspond to administrative areas or cities within a country, state, or other first-order administrative division. The number is usually based on the first filing word in the established place-name form, and is used with classification numbers ending with 2 or 7, 3 or 8, and 4 or 9. The geographic cutter may be followed by a subject cutter.

After the class number, the other elements of a call number include cutters and the date. If you are interested in learning more about those elements, consult the Cartographic Resources Manual for detailed breakdowns.

For a further breakdown of geographic cutters that come directly after the class number when needed, consult the Geographic Cutter Guide and see the second example below.

Let’s look at a map record, find the call number, and break it down: Martin Waldseemüller’s Universalis cosmographia secundum Ptholomaei traditionem et Americi Vespucii aliorumque lustrationes world map from 1507 is a great first example.

Scroll down to the bottom of the record and find the call number: G3200 1507 .W3.

G3200 = Class number. G is for Geography. The number 3200 represents the world.
1507 = Creation date. Ideally transcribed from the work.
.W3 = Cutter number to indicate the creator.

That example was straightforward. Now if you are ready to move on and be challenged, let’s look at a more complicated example: Texas General Land Office’s Brazoria County map, which shows a specific county in the state of Texas from 1877.

Scroll down to the bottom of the record and find the call number: G4033.B7 1877 .T4.

G4033 = Class number. G is for Geography. The number 4030 represents the great state of Texas. The additional 3 at the end in 4033 represents a county in Texas—any county. We can indicate the county depicted in the map by the geographic cutter following the punctuation after the class number G4033.B7. Using the geographic cutter reference tables in LCC, Under Texas. Counties we find that the B7 is unique for Brazoria County.

1877 = Creation date. Ideally transcribed from the work.

.T4 = Cutter number to indicate the creator.

Keep in mind that each call number must be unique. In areas with robust holdings, call numbers will get more complicated to ensure each object has its own unique number and location.

In practice, users search the LC Catalog for an item and identify the call number in the item record. They should write it down, and provide the call number to reference staff, who will use the number to find and retrieve the map in the stacks. Also, users can browse the LC Catalog by call number for other maps covering the same area. In the advanced search function of the catalog, select Browse from the tabs at the top of the page (next to the binocular icon) and select Call numbers and classifications from the drop-down menu. You can then add the class number to find maps.

Below is a de-coding table to familiarize users with the base class numbers for the World.

Geographic Area	Map base	Atlas base
Universe. Solar System	3180	1000
Celestial	3190	1000
Moon	3195	1000
Individual Planets or Moons (other than Earth’s moon)	3160	1000
World	3200	1001
North America	3300	1105
South America	5200	1700
Europe	5700	1790
Asia	7400	2200
Africa	8200	2445
Australia	8960	2750
Antarctica	9800	3100
Oceans	9000	2800

 

Below is a de-coding table to familiarize users with the base class numbers for the United States and its Territories.

Geographic Area (United States and Territories)	Map base	Atlas base
Alabama	3970	1340
Alaska	4370	1530
American Samoa	9560	2980
Arizona	4330	1510
Arkansas	4000	1355
California	4360	1525
Colorado	4310	1500
Commonwealth of Northern Mariana Islands	9410	2905
Connecticut	3780	1240
Delaware	3830	1265
District of Columbia	3850	1275
Florida	3930	1315
Georgia	3920	1310
Guam	9415	2910
Hawaii	9700	3000
Idaho	4270	1480
Illinois	4100	1405
Indiana	4090	1400
Iowa	4150	1430
Kansas	4200	1455
Kentucky	3950	1330
Louisiana	4010	1360
Maine	3830	1215
Maryland	3840	1270
Massachusetts	3760	1230
Michigan	4110	1410
Minnesota	4140	1425
Mississippi	3980	1345
Missouri	4160	1435
Montana	4250	1470
Nebraska	4190	1450
Nevada	4350	1520
New Hampshire	3740	1220
New Jersey	3810	1255
New Mexico	4320	1505
New York	3800	1250
North Carolina	3900	1300
North Dakota	4170	1440
Ohio	4080	1395
Oklahoma	4020	1365
Oregon	4290	1490
Pennsylvania	3820	1260
Puerto Rico	4970	1630
Rhode Island	3770	1235
South Carolina	3910	1305
South Dakota	4180	1305
Tennessee	3960	1335
Texas	4030	1370
Utah	4340	1515
U.S. Virgin Islands	5010	1640
Vermont	3750	1225
Virginia	3880	1290
Washington	4280	1485
West Virginia	3890	1295
Wisconsin	4120	1415
Wyoming	4260	1475

 

Looking for maps at a library using the Dewey Decimal System, don’t despair! The Dewey Decimal Map of the United States—a pictorial map of the United States, showing the Dewey Decimal Classification numbers for each state, as well as major industries within each state—will help you navigate that classification system.

Next time you are on Capitol Hill, stop by the Geography and Map Reading Room and take a stab at dissecting map call numbers. Just make sure you bring a valid Reader’s Card.

For more information check out these other guides and posts:

• For more on cataloging cartographic materials see the Research Guide Cataloging Cartographic Materials by Richard Devery, Collections Librarian in the Geography and Map Division.
• For more on searching the LC Catalog, check out the post, Mapping the Way through the New Catalog by Carissa Pastuch, Reference Librarian in the Geography and Map Division.