I hadn't seen this anywhere so I thought I would post to let people know who were not aware of this. In my last game, I had a city in a northern area surrounded by tundra and ice. There was a river running past, and I found my workers were able to improve the ice tiles along the river with watermills. They gave only 1 hammer initially, but this improves with various techs, and with state property you can actually get food from them. They made a big difference to the city in question in terms of its growth and production capacity.

This is because terrain special features (forest, river, mountain, resources, etc) trump the non ability of being able to improve ice and tundra. This is why you can build lumbermills and camps and things in the tundra and apparently windmills along a river in the ice (although I don't believe I have encountered a river through ice). Makes sense and its good to know.

On a similar note, I find that if you have to place a city in a low value area with desert or ice, its best to place it on an unimprovable tile with little or no yield. Because with few exceptions, the city will produce the same amount anyway, but rather than making one of your few improvable tiles unimprovable, you're making a worthless tile produce something. I'll try to position a city to take advantage of that even if the little blue recommended circle suggests an adjacent tile.

Because with few exceptions, the city will produce the same amount anyway

Actually, I believe there are no exceptions to that. A city square always produces 2 food, 1 hammer, 1 commerce regardless of the terrain it is sitting on. And I agree to your main point of placing cities on unimproveable terrain, I do the same thing :)

Actually, I believe there are no exceptions to that. A city square always produces 2 food, 1 hammer, 1 commerce regardless of the terrain it is sitting on.
Just for the record, a city on a Plains Hill will produce an extra 1 Hammer, and a city founded on a resource will get the base (unimproved) bonus provided by that resource.

i.e. a city directly on top of Rice would give 3F/1P/1C

Just for the record, a city on a Plains Hill will produce an extra 1 Hammer, and a city founded on a resource will get the base (unimproved) bonus provided by that resource.

i.e. a city directly on top of Rice would give 3F/1P/1C

Hmm I wasn't aware of that. Thanks for the info!

This is because terrain special features (forest, river, mountain, resources, etc) trump the non ability of being able to improve ice and tundra. This is why you can build lumbermills and camps and things in the tundra and apparently windmills along a river in the ice (although I don't believe I have encountered a river through ice). Makes sense and its good to know.

Hmm, but that doesn't explain why you can build farms on tundra tiles adjacent to a river (and on tundra only there!), but not on ice tiles near a river.

Farms can only be built on tiles that already produce food (they increase yield, they don't produce it themselves). Tundra has one base food, desert/ice does not. Why you can't build farms on non-fresh tundra is another question.

The same goes for cottages: they only can be built on tiles that already produce food. Which is why you can build them on grassland hills... they start out at 1/1/0.