The following section includes information on a variety of biomes found on planets. Some planets could be entirely made up of a single biome, such as desert or forest worlds, while other planets contain a mix of the following terrain types.

Aerial Terrain

On worlds where the atmosphere expands high above the physical boundaries of the surface, there exists a region of open air. Similarly, gas giants are made up of nothing more than a vast atmosphere, held in place by a starlike core. The most common rules sections to reference when using aerial terrain are Falling, Gravity, Suffocation and Drowning, and Weather. The rules for flying with the Acrobatics skill are also critical for many creatures operating in an aerial environment.

Clouds

Most clouds are little more than condensed gas that obfuscates vision. Treat a cloud in an aerial environment using the same rules as fog cloud, except it's a nonmagical effect. Other types of cloud exist, such as corrosive or toxic clouds, which operate in the same manner as those types of atmospheres.

Stealth and Detection in Aerial Terrain

How far a character can see in the air depends on the presence or absence of clouds. Creatures can usually see 5d8 x 100 feet if the sky is completely clear, with minimal clouds (or other aerial objects) blocking their views. Clouds generally provide enough concealment to hide within (though the hiding creature might have difficulty seeing out from its hiding place).

Aquatic Terrain

Aquatic terrain can be one of the least hospitable to PCs because most can't breathe underwater. The ocean floor holds many marvels, including undersea analogues of any of the other terrain elements described in this text, but if characters find themselves in the water because they were bull-rushed off the back of a transport ship, the kelp beds or volcanic vents hundreds of feet below them don't matter. The most common rules sections to reference when using aquatic terrain are Suffocation and Drowning and Underwater Combat. The rules for swimming with the Athletics skill are also critical for many creatures operating in an aquatic environment.

Deep Water

Lakes and oceans simply require a swim speed or successful Athletics checks to move through (typically, DC 10 in calm water, DC 15 in rough water, DC 20 in stormy water, and DC 30 in maelstrom water). Characters need a way to breathe if they're underwater; lacking that, they risk drowning. When underwater, characters can move in any direction, including up and down.

Extreme Depths

At certain depths, the pressure of the surrounding water becomes so great that characters might be affected as if they were in a thick or severely thick atmosphere, even if they can breathe underwater.

Stealth and Detection Underwater

How far a character can see underwater depends on the water's clarity. As a guideline, creatures can see 4d8 x 100 feet if the water is clear and 1d8 x 10 feet in murky water. Running water is always murky, unless it's in a particularly large, slow-moving river. It is hard to find cover or concealment to hide underwater (except along the sea floor).

Desert Terrain

Desert terrain exists in cold, temperate, and warm climates, but all deserts share one common trait: very little precipitation. The three categories of desert terrain are tundra (cold desert), rocky deserts (often temperate), and sandy deserts (often warm). The most common rules sections to reference for adventures in these areas are Cold Dangers, Heat Dangers, Starvation and Thirst, and Weather.

Stealth and Detection in the Desert

In general, the maximum distance in desert terrain at which a creature can succeed at a Perception check to detect the presence of others is 6d6 x 20 feet; beyond this distance, elevation changes and heat distortion in warm deserts makes sight-based Perception checks impossible. The presence of dunes in sandy deserts limits spotting distance to 6d6 x 10 feet. The scarcity of undergrowth or other elements that offer concealment or cover makes using Stealth more difficult.

Forest Terrain

A forest can be composed of more than trees. On some worlds, vast fungal growths tower into the sky, while on others metallic veins rise from the ground and connect in spidery canopies. Common rules sections to reference for forests are Catching on Fire, Falling Objects, Smoke Effects, and Vision and Light.

Trees

Most forests are filled with trees, or something akin to trees, which provide partial cover to those standing in the same square as a tree. An average tree has an AC of 4, a hardness of 5, and 150 HP (see rules on smashing an object). A successful DC 15 Athletics check is enough to climb most trees.

Undergrowth

Fungal blooms, vines, roots, and short bushes cover much of the ground in a forest. Undergrowth counts as difficult terrain, provides concealment (20% miss chance), and increases the DCs of Acrobatics and Stealth checks by 2. Squares with undergrowth are often clustered together. Undergrowth and trees aren't mutually exclusive; it's common for a 5-foot square to have both a tree and undergrowth.

Stealth and Detection in a Forest

In a sparse forest, the maximum distance at which a creature can succeed at a Perception check to detect the presence of others is 3d6 x 10 feet. In a medium forest, this distance is 2d8 x 10 feet, and in a dense forest it is 2d6 x 10 feet.

Because any square with undergrowth provides concealment, it's usually easy for a creature to use the Stealth skill to hide. Logs and massive trees provide cover, which also makes hiding possible.

The background noise of a forest makes Perception checks that rely on sound more difficult, usually increasing the DC of the check at the GM’s discretion. 

Hill and Mountain Terrain

Hill terrain describes rises in the immediate area, often multiple hills spread over miles. This type of terrain can occur in any other biome. Mountains are steeply rising rock, metal, or even the organic crust of the planet. The most common rules sections to reference when using hill and mountain terrain are Cold Dangers, Falling, and Weather.

Chasms

Usually formed by natural geological processes, chasms are common dangers in mountainous areas. Chasms aren't hidden, so characters won't (usually) fall into them by accident. A typical chasm is 2d4 x 10 feet deep, at least 20 feet long, and anywhere from 5 to 20 feet wide. It usually requires a successful DC 15 Athletics check to climb the wall of a chasm. In mountain terrain, chasms are typically 2d8 x 10 feet deep.

Rock Wall

A vertical plane of stone, a rock wall requires one or more successful DC 25 Athletics checks to ascend. A typical rock wall is from 2d4 x 10 feet tall to 2d8 x 10 feet tall.

High Altitude

At particularly high altitudes, the thinning atmosphere poses a challenge for many creatures, with the same effects as a thin atmosphere. A creature residing at a high altitude for 1 month becomes acclimated and no longer takes these penalties, but it loses this benefit if it spends more than 2 months away from high-altitude terrain and must reacclimatize upon returning.

Stealth and Detection in Hills and Mountains

As a guideline, the maximum distance in mountain terrain at which a creature can succeed at a Perception check to detect the presence of others is 4d10 x 10 feet. In hill terrain, the maximum distance is 2d10 x 10 feet. It's easier to hear distant sounds in the mountains. The DCs of Perception checks that rely on sound are usually lower at the GM’s discretion.

Marsh Terrain

Two categories of marsh exist: relatively dry moors and watery swamps. Both are often bordered by lakes, which are effectively a third category of terrain found in marshes. The most common rules sections to reference for marshes and swamps are Suffocation and Drowning, Underwater Combat, and Weather (see below).

Bogs

If a square is part of a shallow bog, it has deep mud or standing water of about 1 foot in depth. It counts as difficult terrain, and the DCs of Acrobatics checks attempted in such a square increase by 2.

A square that is part of a deep bog has roughly 4 feet of standing water. It counts as difficult terrain, and Medium or larger creatures must spend 4 squares of movement to move into a square with a deep bog, or characters can swim if they wish. Small or smaller creatures must swim to move through a deep bog. Tumbling is impossible in a deep bog.

The water in a deep bog provides cover for Medium or larger creatures. Smaller creatures gain improved cover. Medium or larger creatures can crouch as a move action to gain this improved cover. A creature with this improved cover takes a -10 penalty to attacks against creatures that aren't underwater.

Deep bog squares are usually clustered together and surrounded by an irregular ring of shallow bog squares.

Stealth and Detection in a Marsh

In a moor, the maximum distance at which a creature can succeed at a Perception check to detect the presence of others is 6d6 x 10 feet. In a swamp, this distance is 2d8 x 10 feet. Vegetation and deep bogs provide plentiful concealment (20% miss chance), so it is possible to use Stealth to hide in a marsh.

Urban Terrain

Urban terrain can be found in most settlements where the people have greatly exerted their influence over the surrounding environment, constructing buildings where they can live and work in comfort and laying well-defined roads, usually paved. This type of terrain can occur in just about any biome, and it often supersedes the environmental effects of that biome. Urban terrain can include space stations, and it is often replete with technology. The most common rules sections to reference when using urban terrain are Settlements, Structures, and Vehicles, as well as Breaking Objects and sometimes Radiation.

Stealth and Detection in Urban Terrain

In a settlement with wide, open streets, the maximum distance at which a creature can succeed at a Perception check to detect the presence of others is 2d6 x 10 feet. In a settlement where the buildings are more crowded, standing close together, this distance is 1d6 x 10 feet. The presence of crowds might reduce this distance.

Thanks to twisting side streets and vehicles that can provide cover, it's usually easy for a creature to use Stealth to hide in a settlement. In addition, settlements are often noisy, making Perception checks that rely on sound more difficult, usually increasing the DC of the check at the GM’s discretion.