Culture borders

[Renata]

Can anyone explain how cultural borders work when there's a competition going on over tiles? I can't figure it out. For instance, in my last game, I conquered half of Spain, leaving them only one small city on the same continent and a few more on an island. The continental city (Valencia) was three tiles east and one tile south of Madrid, which was now in my possession. Valencia initially had size-2 borders, and retained them even after Madrid had expanded a couple of times -- so the two shared tiles between the two cities stayed in Spanish control.

Ok, so far so good. Where it gets puzzling is a bit further down the line. I discovered aluminum on the hill tile immediately SE of Madrid; it was my only source. A short while later Valencia's culture pushed out, taking two tiles away from Madrid's first ring: a water tile due east, and the aluminum tile.

Again, so far so good. I switched some specialists hoping to get a great artist of my own, and moved in troops as a backup plan for reclaiming that crucial tile. What confuses me is what I noticed a few turns later -- a water tile north of Valencia was in my control, despite it being closer to Valencia than to Madrid, and despite my having no other cities that could possibly be influencing it (Madrid was my furthest northeast, and the nearest to the southeast and west were each about eight tiles away from the water tile in question.)

So how did I have control of that tile? It gets even more confusing, though. I did get my great artist, and dropped the culture bomb in Madrid. Borders immediately pushed out, grabbing ... a couple of land tiles halfway between the two cities, but *not* the aluminim and water tiles immediately adjacent to Madrid. Next turn I got the aluminum back, plus a couple of tiles next to Valencia, but not the water tile. Turn after that I got the water tile back, and Valencia was down to one land tile. A few turns after *that*, Valencia was working only ocean.

Anyone can tell me what's going on?

 

[Volar]

Ok, hover your mouse over the the name of your city during gameplay. You see a Culture: #####/50000, or something to that effect. If your city has a higher culture, it'll slowly take of tiles, even a city if you have that feature enabled. If not, it'll still cause revolts, that are friendly towards your civilization.


Here's something interesting though. I did an 18 civ game in coop with a friend. I was Russia, and he was France. Due to his city where Berlin would usually be, becoming to powerful, and getting to many wonders while I rushed settlers, it was enroaching on, and hurting St. Petersburg. Well, I had lost 2 tiles, from where our border had been early on in the game. Apon making a permanent alliance, our borders reverted back to their earlier form. Very interesting. Pity they didn't include a system for influence limitations, as a diplomatic option.