During the next century more than half of the world's inhabitants will reside in cities. The rapid growth and urbanization of the world's population are the result of many complex economic, social, demographic, and political factors and pose unprecedented challenges to the functioning of human settlements and the quality of life for their inhabitants.
Urbanization has many beneficial aspects.
Cities play an increasingly vital role in education, culture, and productivity. The process of urbanization is also a significant factor in the worldwide demographic transition to lower birth rates. However, cities throughout the world suffer from a host of problems, including congestion, pollution of air and water, inadequate water supplies, wasteful use of energy, problems of waste disposal, inadequate housing, the spread of communicable diseases, and the deterioration of social support systems. Many cities have expanded into areas prone to earthquakes, floods, and other natural disasters. Even those cities which are no longer growing in population continue to expand in territory, dwelling space, transportation density, resource consumption, and production of wastes.