This has a lot of answers and can be different for the type of game you are running.
First you have geological - I have found it best to handle it by distance, drawing a circles around my campaign area. A days travel will have a good bit of detail but the further out you go, the less knowledge is provided. That way I do not box myself in and can build details as my players explore the world.
Next is Cultural - What is the culture of the campaign area? Things like days of the week, holidays, gods, rulers, coinage, language, common laws, etc... Some of this is more common that others and you may want to rank what is more common than other things, like knowing all the children of the local king or every god.
Now comes Fringe - What things touch the campaign area and bleed over to it? This is hearsay, rumor, gossip that is based on the far reaches of the map.