1. Natural restrictions bewteen provences i.e mountain passes,
flooded gorges. etc
2. Imposed Restrictions within a provence i.e. town wallls.
3. Imposed restrictions at one end of a natural restriction. i.e.
a fort at one a mountain pass.
The first one is doesn't really pose a problem as it seemed to be work
well in olympia.
The second would imply the need for interior features within a provenace.
The first level of this interior feature could be a walled town. This would
mean that people would need to move to the provence and then to the
interior feature. Therefore if they arrive at a proveance and find the
gates shut they can still live outside the walls.
The third restriction could be a headache to install and run as the fort
would need to be within the provence and attched to the route. This would
mean that people moving to that provence would bounce at the fort and not
be able to enter the provence beyond.