Resources are special commodities found in limited quantities on the map. When a resource is "worked" (or accessed), it provides a bonus for your empire; this is accomplished either through constructing a specific improvement with a Worker (on land) or expending a Work Boat (for sea tiles). Bonuses vary from increased yield (production, food, etc.) to a number of units of Iron, Uranium, Gold or some other strategic or luxury resources necessary for producing specific units and buildings, and for providing more happiness to your citizens.