Cities are your sole instrument for developing natural resources and channeling them toward expansion, technological progress, and warfare.
A city is created when Settlers are given the "build city" command on suitable terrain, removing the unit from play to provide the city with its first citizens. A city may grow to include dozens of citizens, some working within the city while others are dispatched as new settlers. Famine, war, and plague kill citizens and reduce population; with the loss of its last citizen a city disappears.
While city growth should usually be your aim, it comes with challenges. As cities grow, managing happiness becomes a problem; this is described in its own section. Pollution (described in the Terrain help), plague, and migration can also be issues.
Each city may work the terrain within its reach. This is a fixed radius of approximately three tiles, giving access to 20 tiles on rectangular maps, in addition to the city center tile.
To extract resources from a tile, you must have a citizen working there. You cannot begin working a tile which a neighboring city is already working, nor can you work terrain upon which an enemy unit is standing, or terrain inside another player's borders. Thus you can simulate conditions of siege by stationing your units atop valuable resources around an enemy city. Units can also be ordered to pillage, which damages improvements. Worker units could even transform the terrain to make the tile less productive.
The section on Terrain describes how the output of each tile is affected by the terrain, the presence of special resources such as game or minerals, and tile improvements built by units. Note that the tile on which the city itself rests -- the city center -- gets worked for free, without being assigned a citizen. The city's tile may also receive other benefits. It always produces at least one food and one production point regardless of terrain; gains whatever advantages the terrain offers with an irrigation system (because cities come with water systems built-in); and is usually developed with roads.
The roles of citizens are controlled from the City dialog. Citizens working the land are represented by three numbers showing their output on the tile they are working. Tapping on these numbers will remove the citizen from the tile, turning them into a specialist (see the section on Specialists for more details); this can be seen in the row of citizen icons. You can tap another tile to assign the citizen to work it, or tap on the specialist icon to change their specialist role.
Tapping on the city center tile in the city map will automatically choose citizen roles and tiles to work, with an emphasis on food production and hence growth. Citizen roles are also automatically assigned when a city grows; you may want to inspect cities that have just grown and adjust the role in which the new citizen has been placed.
Citizens have a nationality distinct from that of the state they inhabit. When a city grows due to food surplus, new citizens take the nationality of the city's current owner, but when a city is conquered or otherwise transferred, its citizens retain their original nationality, as do any immigrants. Units founding or contributing citizens to a city can also bring their own nationality.
Citizens of another nationality will work in your cities just the same as your own, and behave the same in most respects, but they may become unhappy when you are at war with their associated state; their presence makes it cheaper for their state's agents to incite revolt in your cities.
Cities may be enhanced with a wide variety of buildings, which can improve their productivity, their military strength, or give them new abilities. See the sections on City Improvements and Wonders of the World for more information.
- Happiness
Keeping your citizens happy (or at least satisfying) is one of the most important objectives. When your citizens become unhappy, your cities will fall into disorder, which disrupts production; but when your citizens are happy, your cities will celebrate, and your production will increase greatly.
Each citizen working the land is either happy, satisfying, unhappy, or angry. The normal state of a working citizen is satisfaction. However, as your cities grow larger, crowding causes citizens to become unhappy. Each citizen in a city after the fourth will be generated unhappy, instead of satisfying.
If the number of unhappy citizens in a city exceeds the number of happy citizens, the city falls into disorder. A city in disorder produces no food or production surplus, science, or taxes; only luxury production remains. Cities which are in disorder are also easier for enemy agents to incite to revolt. Prolonged disorder under certain governments can lead to a spontaneous national revolution, overthrowing your government.
It should be stressed that only citizens working the land vary in morale -- specialists enjoy enough privilege to remain perpetually satisfying (see the section on Specialists). Thus one solution to the problem of an unhappy citizen is simply to assign that citizen to the role of a specialist. But if cities are ever to work more than four terrain tiles at once, the problem of morale must be confronted more directly.
There are many ways of making unhappy citizens satisfying, which does prevent disorder but is without further benefit. Producing happy citizens can balance the effect of unhappy citizens and also bring other benefits.
Cities that are sufficiently large celebrate when at least half their citizens are happy and none remain unhappy. The effects of celebration vary; they depend on your government type:
- Under Anarchy or Despotism, you will not suffer the normal production penalty for tiles which produce more than 2 points of any resource (food, production, or trade).
- Under Monarchy or Communism, your city will gain the trade bonus of Republican/Democratic governments: 1 bonus trade point in any tile which already produces at least 1 trade.
- Under a Republic or a Democracy, your city will enter "rapture": its population will increase by 1 each turn until there is no excess food or until the number of happy citizens is no longer sufficient for celebration. Without rapture, large cities can grow only by struggling to produce a food surplus -- which can be difficult enough -- and then waiting dozens of turns for their granary to fill.
In small empires, as already stated, the fifth citizen in each city is the first unhappy one. As you gain more cities, this limit actually decreases, to simulate the difficulty of imposing order upon a large empire. The precise thresholds depend on government type; see the section on Government for details.
Thus, you may find that founding or conquering a city triggers widespread disorder across your empire. Continued empire growth may lead to further penalty steps. In empires that grow beyond the point where no citizens are naturally satisfying, angry citizens will appear; these must all be made merely unhappy before any unhappy citizens can be made satisfying, but in all other respects behave as unhappy citizens.
Luxury makes citizens happy. For every two luxury points a city produces, one satisfying citizen is made happy (if there are no satisfying citizens left, unhappy citizens become satisfying then happy). Each city receives back some of the trade points it produces as luxury points according to your empire's tax rates; see the section on Trade. Luxury points may also be produced by other means, such as entertainer specialists.
There are several city improvements that will make satisfying those remaining citizens that are unhappy due to crowding, such as Temples and Colosseums. Some wonders of the world can also have this effect. See the appropriate sections for details.
Military units can affect city happiness. Under authoritarian regimes this is helpful, as military units stationed in a city can prevent unhappiness by imposing martial law. However, under representative governments, citizens become unhappy when their city is supporting military units which have been deployed into an aggressive stance. This includes units not inside your national borders, a friendly city (including the cities of your allies), or a suitable base within three tiles of a friendly city; however, certain units ("field units") are inherently aggressive and cause unhappiness regardless of location.
If you are at war with a civilization and some of your citizens are of that nationality, those citizens may also become unhappy.
These forms of unhappiness are distinct from that caused by overcrowding, and cannot be offset by luxuries, or by most city improvements. Police Stations and the Women's Suffrage wonder can offset unhappiness caused by units, and only a few wonders -- such as J.S. Bach's Cathedral -- can offset any kind of unhappiness, even that caused by military or diplomatic tensions.
- Plague
When plague strikes a city, its population is reduced by one. Unless action is taken to reduce the risk of plague, this tends to act as a natural limit on city size. The game will typically have city improvements or other means to reduce the risk of plague.
The risk of plague depends on city size (overcrowding leads to insanitary conditions) and on the pollution generated in a city. Also, plague can spread via trade routes (without regard for nationality); after a city has been struck by plague, it will remain infectious to its trade partners for several turns, increasing the risk of plague in those cities by a factor depending on the size of both cities.
- Migration
Migration is the movement of citizens from one city to another based on the relative attractions of living in each city.
Every few turns, a citizen of each city in the game may migrate to a nearby, more attractive city, either within the same nation or even across national borders (to a lesser extent, by default).
You cannot directly prevent or direct the migration of citizens. However, you can influence the attractiveness of your cities. The following factors affect the perceived desirability of each city, in approximately decreasing order of importance. (Each factor counts for much more in the citizen's current city, as they prefer not to move without a compelling reason.)
- City size.
- The number of happy citizens. (To a lesser extent, unhappy and angry citizens reduce the desirability of a city.)
- Citizens have a strong preference to move to cities of their own nationality.
- The presence of any wonder in a city will greatly increase its desirability (further wonders do not contribute except by the lesser effect of their build cost).
- Capital cities are more attractive than other cities, all other factors being equal; in addition, citizens will never migrate out of a capital city.
- A high risk of plague reduces a city's attractiveness.
- Food surplus. (A food deficit reduces the desirability of a city.)
- Cities that are further away are less desirable.
- Trade surplus.
- Luxury and science output.
- The quantity of city improvements (and wonders), measured by build cost.
- A number of other factors such as government type and city improvements may increase or decrease the desirability of cities; these are noted in other sections of the help.
Citizens will not migrate to cities which cannot increase in size to support them, for instance due to lack of a city improvement such as an Aqueduct.
Migration can even cause cities to be completely abandoned (ownership of any units being transferred to your nearest remaining city). However, cities with wonders will never be disbanded (so the wonder will not be destroyed), and the last citizen from your only remaining city will never migrate to another nation.