How does the game decide which tiles will be grabbed with each cultural border pop?

[vale]

I just finished a game as Ethiopia. My Capital was fairly strong after moving one turn with 2 salt plains and 2 hills in the inner ring.

My question though is about my first expansion city. The inner ring was Mountain, Lake Victoria, a sheep desert hill, 3 more desert hills with the center tile yet another desert hill. The second ring was 4 mountains 3 desert hills 3 grassland hills with no fresh water and 2 flat deserts. It is a great production city but sacrificed picking up another luxury.

Basically the game did everything it could to not pop those desert hills ever despite the fact that I had desert folklore. There were no luxuries or bonuses for it to be grabbing and no reason for it to prefer the grass hills over the desert hills. There was especially no reason for it to prefer flat desert to desert hills. But it did. It may even have been picking up mountains before the desert hills. I can't remember if I had bought the three tiles before that point. It certainly did go after the ring 2 mountains before the ring 3 desert hills.

Honestly, some of the cultural border pop choices seem almost buggy to me. It seems to favor flat desert over flood plains and desert hills which at best is inconsistent and in in reality is usually just flat wrong. Grabbing mountains before any workable tile in reach also seems wrong.

Has anyone dug into what is actually happening with the border pop mechanics? I did a quick search and didn't find anything.

 

[newarkinvaders]

They really do hate building those desert hills , i dont know why and can only offer my sympathies , i often end up buying the desert hills because the culture is so adamantly avoiding them .

Ive also noted that cities will often squank themselves for some resources but will ignore others to continue building a nice circle from the centre

 

[Hieschen]

What annoys me most, is that it is now the second expansion and the umpteenth patch, and still no option to choose the tile ourselves....

 

[Catan_Settler]

It has some algorithm that attempts to simulate a natural border expansion in a somewhat realistic fashion. For example, it likes keep rivers and mountains as borders if possible as they make natural border lines. So if your borders spread out along one side of a river, it will then start picking any tile that is NOT across the river. Likewise with hill and mountain ranges, it will favor growing away from a mountain range towards flatlands because it treats the mountains like a 'natural border.' So yeah, if you want hill tiles in the near term, or to get a tile on the other side of a river, you're gonna have to buy em.