While the Knowledge skills vary pretty well, Local breaks down even further in a campaign setting.  In the Ign'nikhu world, there are at least 2 local options per region.  For example, in the Rin'nikhu region, there's Knowledge (Rin'nikhu Local), Knowledge ( Rin'nikhu Underdark) and Knowledge (Rin'nikhu Sea-floor).  Obviously, if there is no ocean in the region, it can't have a sea-floor local, but almost all regions in the Ign'nikhu world have at least some connection to the Underdark tunnels(Ironically, those that don't do have some ocean).  Some regions are very large or have drastically different cultures in different parts of the region, and thus might have a North Local and a South Local, for example. 

 

A player making a character that's from the Rin'nikhu region, for example, decides to make a rogue.  A DM should inform the player that their Knowledge (local) class skill should only be treated as a class skill for the Rin'nikhu region local options, or possibly the nearby regions, such as The Land of Lights and the Kymm Islands.  But creating a rogue character that was born in the Rin'nikhu region but has Knowledge (Moorelands Local) is a big stretch and would take that character a tremendous amount of travel... more than a starting character should have.

 

As a DM, you have the freedom to change things as you feel fit the game, and if you think that since the party traveled to a new region and the rogue made lots of new connections that he may know more about the region than he otherwise would, you may grant that player eligibility to begin using that region's Knowledge (local) as a class skill.