9.12. In many countries, the urban system is characterized by the overwhelming preponderance of a single major city or agglomeration. The tendency towards population concentration, fostered by the concentration of public and private resources in some cities, has also contributed to the rising number and size of mega-cities. In 1992, there were 13 cities with at least 10 million inhabitants and their number is expected to double by 2010, when most mega-cities will be located in the developing countries. The continued concentration of population in primate cities and in mega-cities in particular poses specific economic, social and environmental challenges for Governments. Yet, large agglomerations also represent the most dynamic centres of economic and cultural activity in many countries. It is therefore essential that the specific problems of large cities be analysed and addressed, in full awareness of the positive contribution that large cities make to national economic and social development. The challenges faced by cities are often exacerbated by weak management capacities at the local level to address the consequences of population concentration, socio-economic development, environmental impacts and their interrelations.