Lab computers (the ones with turrets guarding them) let you grab about 9 overmap sectors centered on the one containing the lab.
The underground portion of the sewage treatment plants has a computer that lets you grab a map of all sewer lines for about the same range.
You may be able to find Fun Stuff (in places covered by the Advanced Guides) that lets you get a complete map of your overmap sector. Those tend to have Nifty Side Effects though.
Currently, there’s no way to get a map of subway stations or subway lines, though. Sorry about that. 