I think that the fourth textbook entry (The one called "The Japanese Writing System 2) has the most helpful description of カタカナ。It has an entire section devoted only to the Katakana alphabet, while the other textbooks describe all the scripts in one section. Even though it doesn't show the difference in how the different alphabets look or are written, it has the most thorough definition of Katakana. It is the only book that explains in more detail the multiple uses of Katakana-- especially the ones that are harder to define, like when an advertisement is trying to "give an impression of sophistication and modernity."
The example of Katakana which I am analyzing was found in a Japanese magazine that I bought, that is a flashy directory or guide of different attractions in Tokyo.
The Katakana reads ショッピングタウンノ! (Shoppingu taunno = Shopping town)
(I will scan a picture and put it up soon )
There is probably a way to say this using words of Japanese origin, but the Katakana uses English words instead. This contributes to the idea that because Japan closed itself off for so long, western words or ideas seem new, fresh, and exciting. While this Katakana does spell out foreign words, it does not exactly fall into that category of usage-- the words are not Japanese words of a foreign origin, but they are English words spelled out in Katakana. This ad uses Katakana to catch the reader's eye by appearing more exciting.
The use of Katakana for advertisements or eye-catching phrases is understandable from an aesthetic standpoint. The hard angles of the characters convey more energy and excitement than the soft, round curves of Hiragana.