I have yet to run across an in depth discussion about how resource control is gained and lost.
In my understanding of resources so far (mainly gained from the animal husbandry and economy dev journals and discussions)
1) You must first research a technology for some resources to appear on the map
2) You must construct a building to utilize these resources
3) The resources a then “shipped” to your cities.
Lets’ take an “ore” mine for example. I am hoping that the building we need to construct resides at the resource site itself and not in our city. If this is so, then I believe the level of influence you have over the location of the mine should influence both shipping time and cost. For instance, if a mine you construct is located in your own lands I would assume the path or road back to your city is well protected. However, if your mine is in neutral territory goods may take longer to arrive because of the danger. Or if the mine is located inside an opposing Kingdom/Empire the goods might take less time to arrive but, cost you more money to transport because they are traveling across someone else’s lands.
This brings up another point. Do you maintain control of your mine if it is located in another Kingdom/Empire’s lands due to influence shift later in the game? I believe you should, but depending on diplomatic relations it might severely limit your production or increase your costs. Also, I believe that you should be given the option to sell your mine whether it is in your sphere of influence or not.
What I hated about CIV4 was that you would lose your ability to build certain units if the enemy’s sphere of influence extended past your resource. I believe GC2 addressed this somewhat with asteroid mining, but I do not feel that system goes far enough. In EWOM, where specific resources will greatly affect your unit production abilities, I think it critical that a resource is yours until the enemy buys it or militarily takes control of it.
Lastly, and on an almost completely different point, wouldn’t it make sense that when you sack a city you would get to keep some of its stored resources? Maybe similar to CIV4 where you could raze a city or take it over and you get differing benefits for each.