Production in Civilization IV refers to one of two things:
- The process by which cities produce science, money, units, buildings, culture, or anything else. Production happens automatically at the end of each turn.
- Hammers (), which are one of the three basic economic inputs found in Civilization IV. Hammers are produced by tiles when they are worked by population in a city.
A city in civil disorder produces nothing, does not gain or lose population, and costs no maintenance. Otherwise, the computations specified below are applied by the game.
Each city has 1 or more citizens. All happy citizens produce something, either via working tiles in the city's workable area, or as a specialist. You can see where population are in a city in the city screen. Tiles that are being worked have a white circle, and also show their tile production with slightly larger icons. Unhappy citizens are shown in red on the right of the screen. Specialists also show on the right, as do super specialists. Super specialists produce various intermediate goods but do not eat any food.
To compute a city's production, the game first adds up the food, hammers, and commerce produced by each worked tile. Additional commerce is added by each trade route that the city has. Commerce is multiplied by just one possible factor: if the civilization is running the Bureaucracy civic, and the city is its capital, then it gets +50% commerce (i.e. commerce is multiplied by 1.5). Commerce is then divided according to the spending sliders, into base forms of science, gold, culture, and espionage.
At this point, multipliers for each particular category are applied. Most multipliers come from buildings (e.g. a Library gives its city +25% science), but multipliers can also come from civics (e.g. Free Religion gets +10% science in all cities). Whatever the source, all multipliers are added together, and then applied to the base amount of the good in question. For example, if a city has a Library and its civilization is running Free Religion, it will multiply whatever its amount of base science is by 1.35 (100% + 25% + 10% = 135%).
Finally, a few subtractions are made. For food, subtractions are made according to population of the city. Each population point eats 2 Food per turn. In addition, if the population is above the city's health limit, each point of population above the limit eats one additional food.
At this point, production is complete. The finished products are then applied to the civilization, the city, or the city's area on a per-product basis. Specifically, here is how products are applied:
- Hammers are added to the city's current production item. If the city is "building" Research, Wealth, or Culture, the hammers are converted 1:1 into science, gold, or culture and added to their total.
- Science is added to the account for the current research item of the civilization
- Gold is added to or subtracted from the civilization's treasury. If a subtraction would result in the treasury being negative, then the spending sliders are auto-adjusted to increase gold, and the civilization's production is recomputed. If the sliders go to 100% gold and the treasury would be still end up negative, then it is set to zero instead, and the civilization goes on strike.
- Espionage is apportioned to foreign civilizations as per the espionage screen, and added to the accounts thereof.
- Culture is added to the city's total, and also infused into all tiles within the cultural range of the city.
- Excess food (if any) is added to the city's food bar; deficits are subtracted. If the deficit would drop the city into negative food, it is set to zero and a point of population is lost to starvation.
Hammers are the means of measuring a tile's (or city's) production potential. There are three primary sources of hammers.
Hammers are produced inherently by these types of terrain:
Additional hammers may be generated by these tile improvements:
Some resources generate hammers. These resources add 1 Hammer to their tile even before they are improved, and they generate more hammers if improved with the proper tile improvement:
Some resources add hammers only when they've been improved with the particular improvement which unlocks the resource: