Terrain is the ground you walk on, the barrier stopping you from falling into the void. It is a single piece that flows throughout the entire map and combines multiple layers to complete what the terrain looks like, as well as what effects it has on the player.
The "Alpha Layer" is the transparency layer that determines if the cosmetics of the terrain layer are switched On or Off. Meaning the texture on the terrain layer is made transparent to allow for entry/exits through this layer for circumstances such as Caves and Monuments. This does not impact the physical properties of the terrain layer.
Example: Gas Station has an underground ditch inside the monument with an underground cave. Instead of modelling the terrain layer to fit around this ditch you apply the Alpha layer to just erase the terrain within the area that the intrusion covers.
If you do not apply the Alpha layer you will end up falling through the terrain into the ditch and be under the terrain.
Monuments/Prefabs handle the physical collision for the terrain layer. So adding Alpha to an area without one of these prefabs will result in a see-through hole that you can stand on and not fall through.
There is a "Terrain Trigger" volume prefab that will replicate this circumstance and remove the collider for the terrain layer, allowing players to pass through. Ensure you use terrain triggers everywhere underground or players will be killed by anti cheat.
Biomes handle a variety of attributes including:
- Character Temperature
- Tree type/model
- Foliage type/model
- Ore Spawning
- Collectable Resource Spawning
- Collectable Food Spawning Although some changes are purely cosmetic, biomes have influence on the gameplay of your map. Having your whole map "Arctic" biome will result in no food/hemp spawns on your map. Keep this in mind when working with your Biome layer. You should try and include all types of Biomes in your map.
All Biomes are painted onto the same layer and therefore cannot be combined/stacked.
Tundra Biome Layer combined with Sand Ground Layer makes Desert.