Metropolitan areas are important for studying economies and societies in Europe, but there's no standard way to define them. This makes it hard to compare different countries. To solve this, researchers in Spain and Italy developed two methods to identify metropolitan areas. These methods work well for polycentric areas with multiple centers. In Spain, they found 75 main metropolitan areas, covering 75% of the population and jobs. In Italy, they found 81 main areas, covering 70% of the population and jobs. These methods can help researchers compare metropolitan areas across Europe.