A call number is similar to an address; it helps you to find an item in a specific spot on the shelf, on a specific floor, in a specific library. Each item has a unique call number based on subject, but items on the same subject have similar call numbers. This means that related items are shelved together, making it easy for you to discover them by browsing the shelves.
The call number is usually located on, or near, the spine of an item.
Reading call numbers
In the catalogue: read call numbers from left to right
BF204.7 .W55 2013 Porter
On the shelf: read call numbers from top to bottom
Library of Congress classification system
The University of Waterloo library, like many university and research libraries, uses the Library of Congress classification system for most collections. See the Library of Congress classification outline to understand how call numbers are created.