Rhine-Ruhr metropolitan region
The Rhine-Ruhr metropolitan region (German: Metropolregion Rhein-Ruhr) is the largest metropolitan region in Germany, with over ten million inhabitants. A polycentric conurbation with several major urban concentrations, the region covers an area of 7,110 square kilometres (2,750 sq mi), entirely within the state of North Rhine-Westphalia.
Source: Wikipedia — Rhine-Ruhr metropolitan region (CC BY-SA 4.0)