In all parts of the world, cities are organised in systems, as a result of the exchanges of all sorts that are carried out in the social, ecological or technical networks they share. On different levels, these interdependencies reveal the emerging properties, structures that are described on the basis of attributes that differentiate between the cities and the different districts of the cities. The diversity in the cities and between the cities results from this dynamic, and contributes to maintaining it. For example, the functional difference between cities that are unequal in their demographic size and their wealth are at one and the same time a consequence and a means of the international division of labour, or again, the gradients of prices in the inner city share the values attributed to centrality, but also the tendencies of spatial segregation of the social groups. Urban geo-diversity, in these dimensions as in those of the historic, architectural, ecological and cultural patrimony of the cities, is without doubt indispensable to the durability of the development. For understanding and improving the quality of life of our societies, geo-diversity deserves at least as much attention as the attention accorded to biodiversity.

Denise Pumain