The expected growth in urbanization in the less developed countries is the result not only of the natural increase in urban population but also of massive migrations of population to these areas in search of employment. It is estimated that the largest cities will grow more rapidly than the smaller cities and some of these are likely to reach proportions which are totally unfamiliar to town planners. In 1950, only four of the fifteen largest cities were in the less developed countries, but this number rose to seven by 1975. It is projected that twelve of the fifteen largest cities will be in the less developed countries by the year 2000. There were only six cities with populations of 5 million and over in 1950 and their combined population was only 47 million; in 1980, there were 26 such cities and their combined population was 252 million. Projections indicate that this number will rise to approximately 60 with an estimated population of nearly 650 million by the year 2000.