Domain

The known worlds can be best organized into a series of regions called "domains". The boundary between domains is indisinct, and mainly defines the difficulty in traveling between worlds by magical means. Two worlds that are easy to travel between would be in the same domain, with difficulty increasing the further they are apart.

Understanding the nature of domains can become even more confusing because the whole of a single world may not be within the same domain or even consecutive domains. Kai-Chi