Population generates tax, and is used to man resources, become troops or support troops.
Each of the following values can be seen by hovering the mouse pointer over the population icon in the Supply tab of the City Overview panel.
Population Limit[]
This limit is a function of the total available space for the population reside within the city. As more Cottages are built or improved, so the Population Limit increases.
Current Population[]
This is the total number of resided troops and workers within the city.
The happier the population is, the closer this value will come to the population limit.
Labour Force[]
This is the number of residents of the City that are gainfully employed as troops or workers. This value can exceed the current population, and in this case it is safe to assume that resources are not working to full capacity.
Over Utilisation[]
When there are more members of the population in the Labour Force than there are in the Current Population, then the overall happiness of the population will decrease, Population Trend will head towards a decline and Current Population will reduce.
This reduction will be from Idle Population first. If you lose all of your Idle population, you will start to lose working population, and your resource output will decrease.
Under Utilisation[]
When there are more members in the Current Population than in the Labour Force, the happiness of the population will increase until it reaches its maximum value (see Tax Rate for more details). This will cause the population to increase, Population Trend will head towards an increase, and Current Population will increase.
This increase will be being added to Idle Population count, this will continue until the population becomes stable.
Idle Population[]
This is the number of residents that are not gainfully employed. Clearly Labour Force plus Idle Population is the current population.
Although not working, this element of the population contributes tax like the labour force. Idle Population are also available for training to build your army.
Negative Idle Population means that you do not have enough population to man all of your resources. Your resource output will be decreased until you increase your population to meet the shortfall.
Population Trend[]
This is the general direction the Current Population value is moving in, it can be upward, stable or downward, indicating population growth, stability or reduction accordingly.
Population is updated every 6 minutes in game. If population is growing then 1/20 of the population limit will be added after 6 minutes, while if population is shrinking 1/20 of the population limit will be lost until stable.
Increasing Population[]
There are a number of things you can do to increase your population. One is to build more cottages. This will raise your maximum # of population. You can also increase your population's happiness. You can do this by reducing your tax rate, increasing your idle population rate, or upgrading your tavern to offset your tax rate. The fastest fix is probably to just build more cottages.
Tax Generation[]
Tax is generated as a function of the Current Population multiplied by the Tax Rate. E.g.: If the population is 1,000 and the tax rate is 15%, then the hourly income will be 150 Gold (I.e.: 1,000 * 15% = 150).
Resource Manning[]
Each Resource generating Building in the Field requires members of the population to run. E.g.: For a level 4 Quarry to run at maximum capacity, 200 workers are required.
As a new resource generator finishes being built, members of the Idle Population become active members of the Work Force, thus Idle Population reduces, while Work Force increases. Should a resource generator be deconstructed or destroyed, the reverse is true.
Population and Troops[]
Each type of Troop created in the City Barracks requires a member of the population to become that soldier. Some troops also require further troops in support of their function. Population is taken from your available Idle Population at the time of training. These members are removed from your pool of Total Population, and will be replaced over time. Trained Troops in your army do not count against your total population.
E.g.: A Militiaman requires only one member of population, while an Archer requires two, the assumption being, one individual is a bowman, while the other works to provide him with a supply of arrows and the occasional replacement bow. When you train 20 Archers, you will temporarily lose 40 members of your Idle Population, until they are replaced over time.