The economic radius is fairly limited for a small city, but automatically increases as the city grows larger. City growth in turn depends on the number of different buildings placed within the city's economic radius. Though military and production buildings do not have to be placed within the radius, they do count for city growth. The number of buildings built inside a city's radius also increases the rate at which Caravans traveling to this city gather Wealth by +1.
The Indians receive a bonus to their cities' economic radius, essentially giving them more space to work with. For the Chinese, new cities start as Large Cities, thus immediately having the advantage of their larger economic radius.
The economic radius, given in tiles:
The radius of two or more cities may overlap, sometimes resulting in ambiguity when placing buildings. However, when trying to place a building, the radius of the city the building would end up belonging to is highlighted.
Buildings which need to be placed within a city's economic radius:
- Lumber Mill
- Wonders except Forbidden City and Red Fort
Woodcutter's Camps, Mines and Oil Wells do not have to be placed within a city's economic radius. However, Woodcutter's Camps and Mines only profit from the production bonus of a Lumber Mill or Smelter if they are placed within the radius of a city with these buildings. The production bonus from Refineries affects the total oil production and is not city-specific.
Military structures never have to be placed within a city's economic radius, although doing so counts towards the building count required for that city's growth.