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.

Natural Wonders
Natural Wonders are a new class of wonders. Unlike traditional wonders, they aren't built by a civilization, but are found on certain tiles in every map. By default, every map has a set number of Natural Wonders depending on the size of the map. All Natural Wonders are impassable except to aerial units, and they all grant a permanent Happiness boost when they're discovered. Natural Wonders can also be worked like any tile, and provide enhanced yields if they're located within a city.

Bonus Resources
Bonus Resources increase the yield of tiles once improvements are built on them. They are the only type of resource that cannot be used for trading.

Luxury Resources
Luxury Resources grant increased yields on tiles like Bonus Resources, but they also grant Happiness to your empire. However, you can only get Happiness from one copy of a Luxury Resource, which means having many of the same resources will have the same effect of having only one. You can still get more Happiness with multiple types of Luxury Resources, while excess Luxury Resources can be traded with other civilizations.

After Gods and Kings, a few Luxury Resources are manufactured by Mercantile City-States instead of being found on tiles. Forming an alliance with or conquering the City-State will let you obtain these resources.

Strategic Resources
Strategic Resources grant bonus yields when improved and can be traded similar to other resources, though they are primarily used for powerful military units. Strategic Resources are unique in that you need certain technologies to reveal them, such as Animal Husbandry for Horses. There is a cap with Strategic Resources depending on how many resources your empire has. Whenever you produce a unit or building that requires a Strategic Resource, one of that resource is consumed. If you run out of that particular resource, you can no longer produce any units that require it. If the units that use Strategic Resources become higher than the number of resources you have in your empire, such as if you obtained some of that resource from a trade that just ended, your units will be inflicted with a drastic combat penalty. Fortunately, you can regain Strategic Resources if a unit that requires it is eliminated. For example, if you used a Horse to produce a Knight and the Knight dies, you regain the Horse you used.