This is my setting:
http://klimt.cns.nyu.edu/~fishman/DnD/setting.shtml
Several areas are detailed. I'll use the Blood Sea as an example, since it's where the PCs are now.
Knowlege (Blood Sea) allows checks for all rumors, etc. that pertain to the whole area. Some DCs are very high, if the rumor pertains only to a specific area. Here are some sample DCs:
DC 10: The Season of Storms lasts from June through December.
DC 15: Marseilles has just completed a Teleport Circle to mainland Luxoria.
DC 20: Goblin raiders have avoided certain islands recently.
DC 25: Elves have constructed a vessel on the back of a Dragon Turtle.
DC 30: Political envoys from the Necromancers have been seen in several capitols.
DC 35: A plague of were-rats has Marseilles under lycanthropic quarrantine until such time as the PCs -- er, authorities can clear things up. The quarrantine is enforced by Elder Elementals summoned for the purpose.
DC 40: The best "antique" (magic item) dealer in Marseilles is Nadia Soleil. She manages the Steam Mephits who work in her family's shop. She's willing to make "discounts" to those who will help her locate First Empire artifacts.
DC 45: The Urraccan ambassador to Luxoria (an adult Green Dragon) recently flew home from Marseilles, apparently quite angry.
Now, if a character uses Knowlege (Marseilles) instead of Knowlege (Blood Sea), all the DCs involving Marseilles are -10, and all the others are +10. If a character has both skills within 2 ranks of each other, all DCs involving Marseilles are -15.
-- N