Can you create a region based on a single map?

[PenangLion1016]

I have difficulties trying to integrate a single map onto a region.
Is there a way to create a region based on a single map, or backtracing the seed of the master region?

E.g. creating a single city, and creating a region that includes the map of that city, but is part of a larger region.

[Yakka]

I have difficulties trying to integrate a single map onto a region.
Is there a way to create a region based on a single map, or backtracing the seed of the master region?

E.g. creating a single city, and creating a region that includes the map of that city, but is part of a larger region.

There's is a way, but need some json coding that bit different.

Edit: spelling mistake.