I haven't gone through in detail for all the Starfleet vessels I know of, but it seems that all Enterprises seen in the TV show and movies have bridges positioned right in the top middle of the saucer section. I am wondering why this is. This seems to be a very vulnerable location, and in at least one instance (ENT episode "Twilight") the bridge's vulnerable location leads to its destruction. It seems like a bad idea to have the bridge positioned there.
I seem to recall Gene Roddenberry had specified this always be the location of the bridge for Starfleet ships. Whether or not this is the case, I still must ask, "Why?"