See a list of map collection call numbers here.

The primary components of a map call number are the area code (area class number) and if a map displays thematic information, a subject code.  The area class number code may be made up of 2 parts and is always the first part of the call number.

First: maps covering the same geographic area will be co-located, ie: they will have the same class number (the first portion of the call number).

Maps of California will all fall within the range 3850 - 3854

Second: the last digit of the class number says something about the type of map:

0 or 5 General maps of whole areas (whole continents, countries, states, provinces).

1 or 6 Thematic maps of whole areas (whole continents, countries, states,).  Note: regions, natural features, political divisions, and cities as described below may have thematic maps but this is not reflected in the area class number.

2 or 7 Regions, natural features, other named places, etc.

3 or 8 Major political division (provinces, counties, districts maps)

4 or 9 Cities or towns maps.

Maps of cities in California are classed at 3854

Third: Specific location 'Cutter' numbers typically are memetic devices that indicate a named place or a regional subdivision. Specific location cutters are always preceded with a period (.)

A map classed at 3852 .N2 would represent northern California

A map classed at 3853 .S3 would represent Santa Barbara County, California.

A map classed at 3854 .L8 would represent the city of Los Angeles, California.

Sometimes specific location cutters include a colon to further define the area.  For instance, a map classed at 3853 .S3:282 would represent a coastal region of Santa Barbara County.

Fourth: when a map has a thematic emphasis it will have a subject cutter composed of a letter, number combination.  Subject codes will never have periods. 

Special categories
B Mathematical geography
C Physical sciences
D Biogeography
E Human and cultural geography. Anthropogeography. Human ecology.
F Political geography
G Economic geography
H Mines and mineral resources
J Agriculture
K Forests and forestry
L Aquatic biological resources
M Manufacturing and processing. Service industries.
N Technology. Engineering. Public works.
P Transportation and communication
Q Commerce and trade. Finance
R Military and naval geography
S Historical geography

Each of these letters has a numeric subdivision that further identifies the map's theme.

A map showing wetlands in the city of Santa Barbara may be kept at:

385 4 .S68 C3
US-California A city A city that starts with 'S' (C):Physical science