Use of topology and satellite images to border urban areas

In the literature about the definition of metropolitan areas, the methodological approaches are divided between formalists (aggregation by density thresholds) and functionalists (aggregation by commuting quotas). The paper proposes a mixed type of methodology to identify urban areas (the core of a metropolitan area). The aggregation threshold of the Local administrative units around a pivot city adopts two factors. The first one is mean brightness, derived from satellite images, while the second one is threshold density as a function of regional mean density. The identified urban area is treated as a connected domain in a topological sense.