Okay, so, the city of Atlantis, being riddled with advanced computers built by the same folk as made stargates and whatnot, has a database. The Ancient database, the people living there call it in the show, to distinguish it from the database they have set up for their own computers. They work on translating it (Elizabeth), they sent as much as they could to the SGC when they thought they were going to be destroyed, and sometimes when they find something in the city -- or of Ancient origin but not in the city -- they see if they can find info in the database on it.
Now, finding information in the database on a specific but unidentified object is generally problematic, because they don't know what to search for, for one thing, and also because figuring out the filing method in the database has posed some difficulty. The Alterans didn't exactly use the Dewey Decimal System.
Planets are a little easier; by the end of the second season they've clearly located a list of planets that have stargates on them, and also orbital 'gates. Much easier to know when to use a puddlejumper and avoid wandering into vacuum that way. We've seen in the show that sometimes the database has notes about various planets, for example if there was an outpost there, if there was some experiment being conducted there, etc. And sometimes, there's nothing. Like in "Doppleganger" --
McKAY: Look, do you have any idea how many Gate addresses there are in the Ancient database that have no accompanying description?
SHEPPARD: Forty-two.
McKAY: No, I think it's a little more than that. Look, I don't really remember. That's not the point. Nothing -- no information at all. I say that has to mean something.
SHEPPARD: Maybe it means there's nothing worth writing about on those planets.
Now, it makes sense for them to check the database when they're choosing planets to explore (as opposed to conducting trade from contacts made on other worlds, although they probably also check it then) and you can bet they've scoured it for stuff like "ZPM factory".
But here's the thing: any entry in the database is a minimum of
ten THOUSAND years old. They are not going to find information about the cultures currently inhabiting any of the planets, because those cultures
were not AROUND back then! And yet in fic after fic after
fic, I see this illogical bit of fanon.
It's irritating. Like a
rash.