A cryptogram is a type of puzzle which consists of a short piece of encrypted text. Generally the cipher used to encrypt the text is simple enough that cryptogram can be solved by hand. Frequently used are substitution ciphers where each letter is replaced by a different letter or number. To solve the puzzle, one must recover the original lettering. Though once used in more serious applications, they are now mainly printed for entertainment in newspapers and magazines.
Other types of classical ciphers are sometimes used to create cryptograms. An example is the book cipher where a book or article is used to encrypt a message.
Cryptograms based on substitution ciphers can often be solved by frequency analysis and by recognizing letter patterns in words, such as one letter words, which, in English, can only be "i" or "a" (and sometimes "o"). Double letters, apostrophes, and the fact that no letter can substitute for itself in the cypher also offer clues to the solution. Occasionally cryptogram puzzle makers will start the solver off with a few letters. The Cryptogram is also the name of the periodic publication of the American Cryptogram Association (ACA), which contains a large number of cryptographic puzzles.
–adjective giving one's name to a tribe, place, etc.: Romulus, the eponymous founder of Rome.
How does that relate to the way that the building is divided?
Could be floor. I'd more naturally say a building like that is divided into floors.