People migrate to the cities in search of both economic security and better social conditions. As the economy of a country develops, its cities develop as centers of industry investment and education, providing plentiful job opportunities for those in search of a higher standard of living. Sydney, Sao Paulo and Frankfurt are all blossoming up to date cities which have urbanized exponentially since the Second World War. A further example is Tokyo, the core for Japan's rapid economic development in the 1960s and 70s; its population grew rapidly as people moved there to find employment, and it is now the most populous city in the world (population 35.3 million).
Not the entire developing nations, however, are ready to deal with such rapidly growing city populations. The dominant problem coupled with overcrowding is poverty and its attendant social deprivations - homelessness, unemployment and insecurity. immigrants to cities from countryside areas are usually the poorest members of urban society, and in many cities are often enforced to live in shantytowns or slums on the margin of the city with no access to clean drinking water or safe sanitation, in cramped and