Human activities are major contributors to global warming and pollution. Cities are growing and concentrate a large portion of these emitting activities, especially through the transport and housing sectors. There is debate on what is the optimal size and density of cities to support economic and social activities in an environmental and health friendly manner. An increasing opinion is that the larger and the denser are cities, the more environmentally friendly they are, for example because of efficiency gains in transport systems, shorter distances for interactions or lesser fragmentation of natural and agricultural land. This conclusion however is confronted with two difficulties. First, we still lack comparable definitions of the spatial extent of cities, which is necessary for ranking many cities and their environmental impacts along population size or density. Second, describing a city as large or dense completely overlooks its internal structure, especially the distribution of densities as one goes away form the main centers and the relative location of uses (in particular artificialized land for human activities and ‘green’ land supporting a variety of ecological and social services). This project will analyze the internal urban structure of 300 European cities, after applying a comparable definition based on land use scaling properties. It will then investigate the scaling with population of internal characteristics of the urban structure (density gradients, network structures, green land) and measured environmental impacts.