EDIT: oops meant to post this in the other thread.
Moderator Action: Moved.
It is always inefficient to kill a citizen working a mined grassland hill.
At size 6, it becomes inefficient to kill off a mined plains hill.
At size 6, it becomes inefficient to kill off a plains forest.
I wanted to just ignore this before, since it has nothing to do with whipping itself, but let me explain why this isn't a useful way to think about it... It seems to make sense, a grassland mine costs 1 food to run and gives you 3 hammers, a 1:3 ratio. Plains hill mines and plains forests have 1:2 ratios.
What about food neutral tiles? Uh-oh, a grassland forest gives you 1 hammer for no food. Actually the division by zero sort of makes sense, in the absence of population caps, you can run as many grassland forests as you want, for infinite production.
This underscores that this way of thinking is most useful when we ignore population caps, ignore food neutral tiles, and our surplus is fixed.
What if you have excess surplus food and a small population cap, do you want to run grassland or plains mines?
What if we have grassland lumbermills? With a 6 food surplus, we can run 6 grassland mines, or run 3 plains mines and 3 grassland lumbermills, for the same production per population.
Here's how I (and presumably Krikkitone and Vale) think about it:
A citizen working a forest gives you 1 hammer, a mine gives you 2 hammers, both regardless of terrain. The terrain can convert your food surplus to hammers in a 1:1 ratio.
Now if we have a fixed food surplus, no lumbermills, and a high enough cap to run everything, grassland mines do seem to be better than plains hill mines. How do I explain this?
We can run more grassland hills than plains hills before the food surplus is spent. Once the food surplus is spent we must use food neutral tiles, which only give 1 hammer per pop at this point in the game. This is not an intrinsic advantage of grassland mines, it is simply budgeting your surplus to run as many 2 hammer tiles as you can.