The gridded population data used in this first step is from the Landscan project developed by Oak Ridge National Laboratory in Tennessee (United States). Core municipalities corresponding to these city cores are identified. Municipalities sending 15% of their resident employed population or more to the core are included in the commuting zones, which thus can be defined as the “worker catchment area” of the uiban labour market, outside the densely inhabited core. The size of the commuting zones relative to the size of the core give a clear indication of cities’ influence on surrounding areas.