Game Manual 2.0/Terrain

===World===
By default, the Freeciv world is made of squares arranged in a rectangular grid whose north and south edges end against the polar ice, but whose east and west edges connect, forming a cylinder that can be circumnavigated. Other topologies are available as a server option. 
Each square contains some kind of terrain, which together form larger features like oceans, continents, and mountain ranges.
===Terrain===
Terrain serves three roles: the theater upon which your units battle rival civilizations, the landscape across which your units travel, and the medium which your cities work to produce resources. We shall consider each role in turn.
====Combat====
Terrain affects combat very simply: when a land unit is attacked, its defense strength is multiplied by the defense bonus of the terrain beneath it, if the terrain offers one. See the page on combat for details, and the catalogue below for which terrains offer bonuses. (Rivers offer an additional defense bonus of 50%,
i.e. the terrain-specific bonus is multiplied by 1.5.)
====Transportation====
Sea and air units always expend one movement point to move one square — sea units because they are confined to the ocean and adjacent cities, and air units ignore terrain completely. Terrain really only complicates the movement of land units. 
With some rulesets, glacier squares are not suitable for travel; land units have a 15% chance per turn of being lost on such terrain, and Triremes risk being lost if they end their turn next to no land or next to Glacier terrain.
* Moving across easy terrain costs one point per square; moving onto rough terrain costs several. The cost of difficult terrains are given in the catalogue below.
* The explorer, partisan, and alpine troops travel light enough that moving one square costs only 1/3 point.
* Other land units move for 1/3 point only along rivers, which are natural features that cannot be altered (except by transforming land to sea and back again), and roads, which can be built by workers, settlers and engineers.
* With the railroad advance, roads can be upgraded to railroads which cost nothing to move along — units can move as far as they want along a railroad in a single turn! Beware that roads and railroads can be used by any civilization, so an extensive railroad system may offer your enemies instant movement across your empire. Railroads cost three settler-turns regardless of terrain.
With the bridge building advance, roads and railroads can be built across rivers. Note that roads enhance trade for some types of terrain, as shown in the catalogue below, and railroads increase by half the production output of a square. Cities always have roads inside — and railroads, when their owner has that technology — which will connect to (rail)roads built adjacent to the city.
====Improving Terrain====
When cities work terrain there are three products, described further in working land: food points, production points, and trade points. These three are so important that we specify the output of a square simply by listing them with slashes in between: 1/2/0 describes a square that each turn produces one food point, two production points, and no trade points.
The catalogue below lists the output of each terrain, both with and without special resources such as gems or minerals. Special resources occur both on land and along coastlines. They are neither created nor destroyed during the game; even if the terrain beneath a resource is transformed, the resource will change to one compatible with the new terrain.
There are three ways to improve terrain. Workers, settlers and engineers can irrigate land to produce more food or build a mine to yield more production points (but not both on the same square). Terrain not suitable for irrigation or mining can often be altered to become more suitable — attempting to irrigate a forest, for example, creates plains which can then be irrigated. Once built, a mine or irrigation system is destroyed by further alteration of the terrain, if the resulting terrain is unsuitable for the improvement. To irrigate land there must exist a water source in one of the four adjoining squares, whether river or ocean or other irrigated land; but once irrigated, land remains so even if the water source is removed.
After Refrigeration has been researched, irrigated tiles can be improved again by building a Farmland, increasing by 50% the food production of the tile if the city working it has a supermarket.
Fortresses and airbases are also terrain improvements. Both take three settler-turns to complete, regardless of terrain. Only workers and engineers can build airbases.
Only engineers can directly transform land, with the results detailed in the catalogue below. Beware that resource specials will only be present when the terrain has its original type (again). For transforming swamp to ocean, one of the eight adjoining squares must be ocean already, and at least three of eight adjoining squares must be land to allow transforming ocean into swamp. The new swamp will have a river if built adjacent to some river square's single mouth.
Note that engineers have two movement points per turn to invest in their activities, and thus complete all improvements in half the number of turns specified in the catalogue. Several units working on the same square under the same orders combine their labor, speeding completion of their project. When a unit's orders are interrupted its progress is lost. This will also happen if the unit's former home city is conquered or destroyed.
===Villages===
The user who hosts the game has the option of including villages, primitive communities spread across the world at the beginning of the game. (Some users also call them huts.) Any land unit can enter a village, making the village disappear and deliver a random response. If the village proves hostile, it could produce barbarians or the unit entering may simply be destroyed. If they are friendly, the player could receive gold, a new technology, a military unit, or even a new city.
===Terrain Catalog===
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Next: Cities
Terrain