When generating a chunk it cannot depend on neighbouring chunks already being generated so it has to be able to calculate things on its own.
It is important to note that this mod cannot depend on any specific order of chunk generation. This makes generation very efficient and also allows it to fit much better when the surrounding world. That means that are generated at the very first stage when a chunk is built. The buildings, bridges, subway system, fountains and other structures you find in the world are actually not structures but real worldgen. In this first section the basic operation of the mod is explained. This page is mostly about the internal structure and configuration about the mod. The world generation is about an abandonded city.
