The Sea of Stars
The Shards stretch through the astral sea, too numerous to count, many linked to small stars made from the magical stone, residuum. You all start out on a cluster of shards, called the 13 kingdoms, which are all given light by the Star Tower, a hollowed-out residuum star that houses the capital city of all the kingdoms, while also being their source of light.
The kingdoms are geographically close, some being connected together by bridges, and all relatively easily accessible by airship. The orbit of the Star Tower brings it closer to each kingdom at various points through the year. Other shards can be reached by perilous journeys through the Astral Seas, or by various teleportation rooms, or portals, but none of these are considered part of the Kingdoms.
While each kingdom has its own governance and autonomy, the Star Tower council has the ability to overrule any action taken by the kingdoms. The kingdoms are incredibly varied, and each has its own politics, governing structure, etc. They do not even all share the same technology.
Several gods still make their home within the 13 kingdoms, while other Demesne’s have been abandoned.