This is a work flow of how I built Torʻs Domain from height map data and painting a grey scale ocean and sea using stereoscopic dept paint techniques.
For actual use in a game the river would have to be to the same level as the water fall and ocean is painted and attention to scale might need far more care to make sure that the rivers and oceans are deep enough yet not so deep that they are bottom less pits.
The actual initial height map which is squashes and stretched to get a proper 1 to 1 ratio is actual height map satalite data of Tibet. I asked years ago and as long as it is an image who controls and image was the response. I shrugged and took it as it was intended. It was a good starting point for height map data that was not already covered in roads and cities.
The idea is to create domains that connect to the domains around them via a border area that is not directly controlled. This creates a political system that allows for people to smuggle good around the borders by getting creative, while allowing for game play that involves creating trade route and right of way grants.
In this example the main domain is one of 1000 player controlled scattered among 10,000 domains, of which initially 9,000 would be under NPC control, and 2,000 would be locked to NPC and story arc.
The idea being that each Domain has a theme and story arc. how the story is advanced is through player quests and expansion packs. Each expansion is a book with so many chapters. When players work through the story in one domain they then have literately 9,999 domains to work through after that. Committing crimes in one Domain sets faction, and can even set NPC and players to be able to kill on sight.
With one border being aligned with another domain there is always a realm verse realm area, but the if the Domains are not at war, the player has to use a portal to the adventure zone or unlock gates between player cites. In the example