We took a vote when we made our PSGs whether balls on the tops of the ISDs were radars or shields. We decided to base our design off the movie (and indeed several games) which all depict the giant domes as shield generators. So, when it comes to the FirstStrike universe (*giggle*) those are, in fact, shield generators.
You decide facts by committee? How very unscientific. Darwin and Einstein roll in their respective graves, and Kent Hovind shits his pants with glee. Next you'll say the FS maps were Intelligently Designed, as opposed to brought about by natural processes.
Indeed I was half disappointed that the shield gen on Ryloth wasn't a huge dome myself.
It wasn't a giant dome because us champions of truth shot your decided-upon-by-committee ideas down, you blackguard of irrational thought, you [waves Nietzsche statue threateningly].

"One of the bitches actually gave birth while she was attacking, and her puppies joined in on the carnage."
--the awesomeness that is Boatmurdered.