Sid Meier's Civilization V/Terrain and Resources

Each map in the game is composed of many hexagonal tiles, each giving a set yield that will be displayed when moving your cursor over it. A city will get this yield when you assign your citizens work it. A tile's yield depends on the terrain it has, the features on it and whether any improvements are constructed on it.

Resources are scattered across the map on certain tiles, and their benefits can be obtained by constructing improvements on it. There are three types of resources. Bonus resources simply increase the yield you get from a tile. Luxury resources provide happiness and can be used to trade with other empires. They also activate We Love the King Day if you improve one that your city desires, giving that city increased Growth. Strategic resources are required for certain military units and buildings, but can also be used for trading.

The terrain of an area is always an important factor to consider when settling cities, since it will decide how productive and profitable the city is, while granting potential military benefits or penalties.

Features
Features exist on various types of terrain, and grants bonus yields to that tile, in addition to certain combat and movement modifiers. Certain types of features like Forests and Marshes can be removed to allow for construction of more improvements or for convenience, but note that they are gone permanently after removal.