What Constitutes a "Strategic Resource" During Combat?

[NakedYoga]

I was attacking Tyre, and I realized that my units were incurring penalties for attacking from strategic resources in very strange circumstances. I was using my ballista to weaken the city's defense, and I noticed I was getting a +25% bonus for my great general being nearby, but also a -50% penalty for being on a strategic resource. The tile simply had a trading post on it. "Okay," I thought, "I'll move to the tundra tile next to this with nothing on it." So I spend 2 turns moving to the unimproved tundra, setting up the ballista, and then when I get ready to bombard the city again, I realize the ballista is still getting the -50% strategic resource penalty. This really doesn't seem to make sense.

Maybe it's a bug? Or am I missing something? Has anyone else run into this?

[turingmachine]

Ballistas need iron. Did you perhaps loose your iron supply? I think resource dependent units get a penalty if you loose access to the resource you built them with.

[NakedYoga]

Ah... haha, wow, you're right. That's the whole reason I was attacking Tyre -- to get their 2 iron mines. I had been their ally previously, and when I lost their iron after our alliance ended, I was at -1 iron. I actually posted about this in another thread; I should have made that connection. I just wish the notice said something different rather than "strategic resource penalty." That made me assume it was saying I was attack from a strategic resource and incurring a penalty based on that.

Thanks.