Here are some common rules used in the building of fictional maps:
* Mountain ranges are formed where tectonic plate movement causes subduction, or where plates collide. These tend to be long structures with occasional valleys and passes. Older mountain ranges will be lower, rounder, and more eroded. Solitary mountains are more likely to be volcanic in origin.
* Rivers always descend downhill, and join with other bodies of water or eventually evaporate. They flow precipitously in mountainous areas, sometimes forming canyons and waterfalls, but tend to meander and build river valleys in lowlands. Rivers often join up, but almost never split, at least until very close to their mouths. The region around a river is usually rich in life.
* Swamps form where the ground is level and there is a large influx of water, such as at a river delta, that drains off slowly.
* A forest will typically form in locations with higher levels of rainfall. Where the prevailing winds cross a mountainous rise, the forest will appear on the windward side where moisture tends to be deposited. The far side will be dryer, and may become desertified.
* Deserts form in locations where the climate conditions limit precipitation. They can occur inland where they are sheltered behind a mountain range, or in regions that receive little humidity due to the prevailing wind conditions. Deserts can occur at any latitude, including the arctic conditions found in a tundra.
* Sentient settlements will normally form in locations where there is a suitable economic need for a population center. This could be a port along a river or coast for trading; a location that is favorable for farming or resource gathering; or a commerce center along a land trade route. Less frequently settlements may form for particular cultural reasons, such as the proximity of a religious site.