The schematic shows the concept of modular construction of vehicles. The lower platform indicates the principle of vehicle assembly in the past where all the components of the vehicle were assembled together on the main assembly line.
Today the trend towards modular assembly is evident, where a entire pre-assemblies are finally mounted on the vehicle on the main assembly line. The individual components of the pre-assembly or module are assembled at different locations.

Automobil Produktion, 1998,
[AUP98g] Grafik BMW