The map file and the sidecar

A Rust custom map is one file, a .map, and it is a complete world: the terrain, every layer, every placed object and every path, in a single compressed container. Creator sometimes writes a second file beside it, a .rcside sidecar, for the things that have no place in the standard format. This page is what is in each, and which of it a server reads.

The .map format is Rust’s, not Creator’s. It is the same file other map editors write, the same file a server downloads, and it is documented here because knowing what is in it tells you what can and cannot survive a trip through another tool.

What a `.map` is

Inside, the world is four things:

Part	What it is
size	The map’s edge length in meters. This is the one number the whole file is scaled to.
maps	The named terrain layers: height, water, splat, biome, topology, alpha. Each one is a square grid covering the map.
prefabs	Every placed object. Each entry is a reference to a Rust prefab plus a position, rotation and scale.
paths	Roads, rivers, rails and powerlines. Each is a line of nodes plus its width, its fades, and which splat and topology it paints.

What each layer does is on How Rust builds a map. To see a layer, or to keep a copy of one, Layer files writes each of them to its own file.

One thing worth knowing about the prefab list:

Monuments are in there like anything else, as a root prefab at a position. The monument’s own contents and its terrain masks come from the game’s assets, not from your map.

Two categories that are baked, and one that is not

Train tunnels and underwater labs are part of the map file.

Trees, ore, collectibles, animals and container loot are the opposite: none of them is in the file, and the server creates them every time it starts, from your biome and topology layers. So a map file is a world plus a rulebook, and the living part is spawned onto it.

Creator’s own data, inside the same file

The standard format has no room for trigger volumes, IO wiring, loot and vending profiles, NPC spawners, custom ziplines, placed vehicles, or a Bradley’s patrol path and the cargo ship’s route. Creator saves those in the .map too, and a stock server ignores them.

The map’s Server upkeep settings are one more such entry, and only while one of them is set: a map whose rows are all at Rust’s own carries no upkeep entry at all.

So one file carries both. On a stock server it loads and plays with those parts inert. Install the server extension and it reads them and applies them. Nothing is lost either way.

Creator keeps other tools’ data in your map when you save. See Import a RustEdit map.

The sidecar

The sidecar is a .rcside file with the same name as your map, sitting beside it. It holds the things that belong to the editor rather than to the world:

In the sidecar	Why it is not in the map
Trigger volumes	They are used only by the server extension.
The recipe a generated map was built from, and the verdict it was given	It is a record of how you got here, not part of the world. A Creator Mode run records its mode and everything it was asked to do (the land, the monuments left out, the pins and the bridge settings), which is how the panel reopens in Creator Mode with the same settings.
Bridge records	The bridge itself is entirely in the `.map`. What the sidecar keeps is what the geometry cannot say, above all the clearance each deck was built to.
Which server a RustEdit map is written for, and anything set aside for that choice	See Import a RustEdit map.
Your camera bookmarks	They are views of the map in the editor, not part of the world.
The link between a live path and the ground it shaped	The map already holds the finished ground and the path itself, which is all a server or a player needs. What the sidecar adds is the ground as it was before the path shaped it, so Creator can put it back when the path moves. It can be megabytes, and every player downloads the `.map`.

Most maps have no sidecar at all, and that is correct. Generate a map in Standard Mode and save it and you get one file. The sidecar appears only when there is something for it to hold, and its absence is never an error.

Keep the two files together. Copy the .map and its .rcside as a pair, to another PC, to a server, or into a backup.
A map without its sidecar still loads and still plays. You lose the editor-side layers, not the world. Nothing breaks. A path that was live is an ordinary path on finished ground: nothing about the ground is lost, only the ability to move the path and have the ground follow.
A sidecar without its map is useless. It is keyed to the map beside it.
To see what differs between two versions of a map, open one and use Compare maps. It compares the two .map files; it does not compare their sidecars.
Give each version its own name. Servers and Rust clients both cache the map they downloaded, so an edited map under the same name can come back as the old one. See Run your map on a server.

Where these files live on your disk, along with everything else Creator writes, is Where your files live.