The five most important regions, collectively often called the "Big Five",[3][4] are frequently compared with other European metropolitan areas for investments and market development.[5] They are (from north to south): Hamburg, Berlin, the polycentric Ruhr-Düsseldorf-Cologne region (collectively referred to as Rhine-Ruhr), Frankfurt and Munich. The Globalization and World Cities Study Group (GaWC) considers Frankfurt to be an "α" (Alpha) global city, while the others are considered "β" (Beta) global cities.[6]