There are two questions involved in this matter. One is the legitimacy of the preposition off of in general, which is discussed in the usage note in this entry in the Merriam-Webster Online Dictionary:"off of" is frowned upon, at least by my mother! For example, we should not say "I got it off of him" but rather "I got it from him". I would go with "based on", no argument.
The other question is the legitimacy of off of in some uses rather than others. Even speakers who use it may avoid it in some contexts. I use it, but would not say, for example, "I borrowed it off of him." That distinction is not mentioned in the M.-W. entry, but can be found in other online sources.usage The of is often criticized as superfluous, a comment that is irrelevant because off of is an idiom. It is much more common in speech than in edited writing and is more common in American English than in British
I don't remember having heard based off of before this thread either. Its use in edited writing, however, can be seen by doing a search of Google Books, and of course its use in writing, edited or not, can be demonstrated by searching the Internet, for example, with searches comparing "based on the book" and "based off of the book".I don't remember hearing based off of before this thread. Off of is discussed here: http://forum.wordreference.com/showthread.php?t=193842&highlight=offe
I do think it's as "bad" as "off of". I'm OK with "working out of..." Someone can be "based in Z city and go out to work in the region around it" Odd? Not so much!Based "out of" is I think an American usage, for instance Thomas Pynchon uses this and variants with "out of" often in his novels, and I have seen it elsewhere. Maybe it is just US military slang (Pynchon was in the navy for a while). "Working out of X Y or Z city" is also used quite a lot in business-speak.
A valiant effort, Michael, but I fear that the distinction is too fine to be useful. I will stick with based in.1. The 7th Fleet is based in Yokosuka ~ the Fleet has a main naval base which is in Yokosuka.
2. The 7th Fleet is based out of Yokosuka ~ same as above, but also used because the Fleet operates all over the Pacific, running operations out of (or "from", but "out of" is a common way of putting it) Yokosuka.