The "Procedural Map" is a type of map in Rust Experimental that is randomly generated. On every server that utilizes the Procedural Map system, no two maps between servers are the same. When the world is initially generated for the first time, the world creator will choose a random number (for example, 37824), which determines the layout of the new world. This number is commonly known as a "seed". The server owners can also select specific options that alter the world generation such as the size of the world. Once the map is generated, it cannot be changed.
Everything is randomized in the initial world generation, including radtown placement, roads, rivers, monuments, and biome placement.
You can view how a map has been generated by using playrust.io