Terrain
From GenieWiki
Terrain is a game term referring to the base upon which all units are placed. Terrain has several properties - it consists of a repeated pattern of a series tile images, and may also include randomly placed trees and other ambient objects. Though these objects are a part of the terrain in the sense of the terrain painting process, they are still normal units and can be deleted, moved etc without affecting the terrain underneath. Besides its appearance, the other key property of a terrain is its passability to units. Most terrain will only admit certain units - for example water is only passable to naval units, while land terrains will (not surprisingly) bear only land units. Shallows terrain is an exception and allows most units to pass, but cannot be built upon. Elevation is the height of a given area of terrain the effect of elevation is mostly aesthetic, but also has a small effect on game dynamics. Additionally, it is impossible to build on slopes. Cliffs, while informally considered to be part of the terrain, are technically units, and are not terrain in the game sense. In the scenario design community, the definition of terrain is also sometimes expanded to refer to all Gaia objects on the map.
Using data editing, terrain restrictions (as described above) can be removed, allowing designers to place objects upon any terrain they desire, with none of the normal restrictions. Beta terrains have been unlocked for both Age of Empires and Age of Kings.
