This approach is called “spiral campaign development,” and it’s a common method of world building. Using the campaign spiral, you build your campaign from the characters’ starting location, filling in the details of immediate interest to the characters and the players, or those that might come up in the next session. You don’t worry about the details of the larger world because you have no idea where in that world the story is going to head. Instead, you focus your attention on the characters, the locations closest to them, and whatever local concerns connect to their direct interest.
