Cologne isn't part of the Ruhr Area, it's part of the "Cologne-Düsseldorf" Agglomeration and the latter was apparently larger than the Ruhr Area when this quiz was made.
This year both these areas merged into the "Rhine-Ruhr" on citypopulation, making it a mega city!
If you want to count it as the rhine-ruhr area, name it like that!
This year both these areas merged into the "Rhine-Ruhr" on citypopulation, making it a mega city!