This is such a great post to read, I've also been thinking a lot about some of these things, and in particular about having a) quantified resources, and b) manufactured resources. I hadn't come to actually write it because my mind is still trying to figure out how it would be good to have this in the game... but here are my thoughts!
To build on what's already been said by makka, manufactured resources one of the most important things that explain differences in development around the world and can help us to have strong post-colonial countries (in Europe, but also Japan, Korea, and the US) despite countries having small territories or having their territory mostly full of grasslands (like Germany).
There are a couple of
manufactured resources that come to mind as first iterations. I'd propose to include porcelain, plastics, electronic products and vehicles. As for steel (and I'd thought of textile fabrics too) the problem is that the major uses of iron and cotton/wool are as steel and fabrics, just like grapes are mostly used for wine making and we don't have both as separate things. Then representing the manufacturing process itself might not be that necessary for these products. All manufactured resources would be tied to particular buildings such as "electronics factory" and "vehicles factory" (and porcelain I think should be tied to China's UB).
Regarding the
location and availability of raw materials, I'd like to propose only having in the map extracted raw materials (anything you get from mines, quarries, fishing and whaling boats, and hunting camps). For all produced raw materials (what you get from farms, pastures, orchards, and plantations), I'd propose to remove most of them from the map, leaving only one per area where they were domesticated (representing wild varieties). Every civ, when they build a farm, pasture, orchard or plantation, gets to choose what to grow there, with two restrictions: 1) that the resource is available there in real life (we can create maps or rules), so that for example coffee can only grow in tropical regions, and 2) that the civ already has access to the resource. A civ would have access to a resource if it's already growing it or if it acquires it through trade.
I'd suggest to
add a resource improvement for sea tiles,
fish farms, to represent aquaculture. This would come late in the game and allow the production of fish, crabs, clams or pearls. I'd also suggest having
quarries buildable on any land terrain except deserts, providing hammers and representing sand, gravel and ground limestone, which are all used as construction materials like concrete. Of course, this comes with the opportunity cost of producing food in the tile. As a fun fact, desert sand is not useful as construction material because it's too smooth due to wind erosion, and it doesn't "stick together" like other sand does – hence my recommendation of not making this available in deserts.
Now, regarding
the quantities produced (for all resources, incl. produced raw materials, extracted raw materials, and manufactured goods), I think productivity (per turn) should be directly related to technology and civics. For extracted resources, we could consider having caps (absolute caps for non-renewables or per-turn caps for renewables. I'm not so sure about this because in practice we can have caps already via tech and civics and while resource depletion is definitely a real problem, it wouldn't matter so much until the very, very late game so that representing isn't as necessary.
I have some doubts on
how to represent consumption of materials, though. Anything that a city produces (in the production queue) such as units, buildings, and wonders could have a cost on resources. For example, building a swordsman would not only require having iron available, but actually consuming some of that iron. But how would that translate to the production of manufactured goods? If vehicles were to be added as one of the manufactured resources, and we were to say it requires the consumption of iron or aluminum, would they be automatically consumed, or only if they are left over? and then how does the civ prioritize when it wants steel for manufactured goods and when to save steel for a navy? My preferred option would be for the civ to have to ask the city to produce this or that manufactured resource, so that a vehicle factory only enables the city to produce vehicles, but only does so when these are in the production queue. The amount of vehicles then depends on the technology level and the civics.
A question I still have is
whether to represent construction materials. Besides marble and limestone, which have specific uses on wonders that we could quantify, we could assume that the game already represents timber and construction aggregates (ie, sand, gravel, ground stone, as I was mentioning earlier) in the form of added hammers from forests and hills, yet these aren't resources per se – they're sort of invisible. I'd imagine that to follow the logic of "building a swordsman costs 1 iron", we'd have something like "building a castle costs 4 stone", but then we could also think of including timber and aggregates (maybe we can call that "cement") in this category. As I said, I'm not sure about this.
As for the
consumption and distribution of food resources, ideally, food should be tradeable, so that civs can send "10 wheat, or 2 wheat per turn" to other civs as part of trade agreements, for cash, or in master/vassal relationships. The more interesting question is how to decide which city within the receiving civ gets the resource and grows. I'd propose that this is tied to security and employment. In other words, cities that are in peace (no revolts or attacks) and have more economic activities (so, more buildings) have priority over those that are insecure or have no employment. Unhappiness (and not sure about unhealthiness?) would act as a cap, with cities that are too densely populated not growing anymore and leaving food to others. Civics should also play a part here. For example, absolutism and central planning, would pull the balance towards the capital and to industrial cities, while agrarianism and feudalism would favor agricultural cities, and external trade civics would favor seaports. Civics should also affect food distribution between core and colony cities.
The interesting thing about this dynamic is that it allows for
food security and industrialization to play much more important roles. The strategy would be for colonizing countries to import food from their colonies to sustain growing populations and then to continue, as industrialized countries with land scarcity, to depend to some extent (as Japan or Singapore do) on food imports to sustain this population. High population means that there should be a high number of worker specialists in the city, which represents perfectly what has happened in the world in the last century or two.
And since we're talking about this, I'd also love seeing
new resources (some of which were already mentioned by makka): potatoes, soybean, olives, oil palm, apples, citrus, pineapple (or another tropical fruit), cocoa, hemp, rubber, timber, seaweed, coral, amber, saltpeper.
Hopefully this will spark some more discussion!
I think colony would be defined as non-core territory on another continent. Though it wouldn't fit that well for a contiguous land empire on multiple "continents" like Mughals owning Persia, or a non-conouldtiguous case like Moors owning Algeria and France. Though we would want it to apply to France owning Algeria!
