Surveyor unit

[DeckerdJames]

At some point there could come a surveyor unit available. You place the unit where you want a city's border to expand, and it is guaranteed to expand there. Perhaps they can be like traders, in that, there is a limit on how many you can have a one time.

 

[Saxo Grammaticus]

I would probably prefer instead to simply prioritize tiles for the city to expand to, representing some sort of claim system. Perhaps it is a leveling tactic for the AI and players to use the same tile expansion mechanic, if indeed that is the case. I also think adding more culture bombs could make the game more interesting by encouraging dynamic borders and cause for conflict.