Can anyone help me figure out the logic behind this so I can attempt it? I'm no amateur but I'm not amazing either, so I'm confident I can do it, just not sure how.

I also know it's a bit of a demanding list but hopefully someone can slog through it.

What I want to do is have a city object with a border around it like in Civilization, however I don't want it on a grid so I can't just draw it over tiles. It's got to be able to grow and expand as the city does, when new buildings are added I want it to push the borders out etc.

I also want the borders of different cities to interact with each other, where the strength of a 'culture' value for example would have one side slowly erode further into the other as it loses influence over the land.

Oh and I also want these borders to be something the mouse can raycast onto or select so the player can interact with them.

The only way I can think of doing this would be creating a 2d plane and adding new points along the mesh during runtime but if I wanted smooth borders the poly count would surely rise like crazy? especially with multiple cities.