All Rust maps (apart from ones that are made by Facepunch and saved as an Unity scene), are stored in a .map file. When first joining a server that is running a procedural map, Rust will generate the map from the following information:
Size (1000-6000) : Seed (0-9999999999) : MapType (ProcGen/Barren)
The map is then saved into a .map file, and can be found in the Rust install directory inside the maps folder. The map filename will be named MapType.Size.Seed.map
Custom maps are essentially a pre-generated map, which is downloaded from an URL rather than being generated based on certain values.
Map files are stored in the format below, and compressed using a LZ4Stream. They first contain the World Serialization number, currently 9 and then the WorldData.
The WorldData is stored in the following format:
The MapData contains a layer (Ground, Biome, Heightmap etc) and the corresponding ByteMap. It is stored in the following format:
The PrefabData contains info on the ID of the prefab, and it’s world space values. It is stored in the following format:
The PathData contains info on the Rivers and Roads of the map. It is stored in the following format:
Information gathered provided by the Rust Map Making community.