I think call numbers confuse the heck out of people. And I’m sorry to hear that, because they are actually a pretty nifty research tool all on their own.
Let me explain.
In the online world, it doesn’t matter where a file (such as a website) actually lives – you can link to it from anywhere. (Google makes its fortune on this very fact, by ranking a site according to how many other sites link to that site.)
Physical objects don’t work that way. They have the unfortunate problem of only being able to be in one place at any given time. Think of going to the grocery store: all the toothpaste sits in one aisle, all the produce is in another, and the frozen goods are somewhere else. You can’t stand in front of the toothpaste no matter where you are in the store (which is how the internet works); you have to stand in the toothpaste aisle (which is how the physical world works).
Books (and other materials in the library) work the same way. They can only sit in one place. Like houses, they have an address – that’s the call number.
Only call numbers are much more powerful than a street address.
Call numbers tell us something about the topic of the book. So, for instance, books on education are shelved in the Ls. Books on psychology are in the BFs. Books on science are the Qs. Books on medicine are in the Rs.
Big stinking deal, right? Wrong! It gets better.
Each call number starts with a letter (or letters) and numbers. Then there’s a decimal point. Then there’s more stuff after the decimal point. It usually looks like this: BQ4022.K46 2000.
If you have a call number for something, you now have information about where to find other items on the same topic. It just so happens that BQ is where we shelve books on Buddhism. So if you found that one call number (BQ4022.K46 2000) and went to the shelves to find that item, you would be standing right in the midst of all the Buddhism books. That’s pretty handy. Now you can start browsing the shelves, just like you are in a bookstore.
The Library of Congress maintains a page where you can view PDF or Word versions of the classification outline. These outlines show you that, for instance, the history of Germany is shelved in the DD call numbers, or books on forestry are shelved in the SD call numbers.
If you want an even more precise breakdown of call numbers, contact me. I have all 41 volumes of the classification outline next to my desk. (!!!)