In both developed and developing countries, cities have been attractive centers to human settlement. As such, the rate of urbanization has been increasingly higher. In other words, the urban population in general and population of cities in particular are growing substantially faster than the total population. Moreover, this differential is widening in several countries. As a result, urbanization continues at a rapid, and sometimes at an accelerating pace. For example1, in 1950, there were only two cities, London and New York, with populations of more than 10 million. By 1994, in the world the number of cities which had populations of more than 10 million were 14 of which 10 were in developing countries. It is also anticipated that there will be 27 largest cities in the world with population of 10 million or more two decades from now, of which 23 will be in developing countries, and only 4 in industrialized countries.