Resource

A resource is a special commodity that gives bonus yields (such as food or production) to its tile. It may also have an effect across the empire or on cities which have access to it, most notably increased happiness.
The number of resources and complexity of the resource system has steadily increased with each new entry in the Civilization franchise. Some resources such as Peat, Pig, and Rubber have appeared in only one game; others such as Crab, Copper, Sugar, and Stone have been in different resource categories depending on which game is involved.
From Civilization III onward, there are three types of tile resources, some with additional effects apart from increased yield:
# Strategic resources, which are required to build certain units and buildings.
# Luxury resources (sometimes called luxuries), which increase happiness.
# Bonus resources, which simply improve tile yield without other effects.
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