The urban population worldwide is growing at a muchfaster rate than the population as a whole, and by larger increments than ever before. Improving social and economic conditions for all people and promoting sustainable development is increasingly an urban challenge. As cities grow, these improvements become increasingly complex (United Nations, 1995). The world’s urban population in 1996 was estimated at 2.6 bilion. Within 10 years more than half of the
world population will be in cities, 3.3 billion of the 6.59 billion total. Urban areas are globally expected to double to more than 4 billion people by 2025, some 80% of them in developing countries.