Large numbers of people have lived in close proximity to each other in cities for thousands of years. The first urban cultures began to develop about 5000 years ago in Egypt, Mesopotamia and India, but the size of cities and their geographical distribution expanded dramatically after the Industrial Revolution of the previous millennium. This expansion accelerated into the twentieth century which began with 13 per cent of the world’s population living in cities and ended with a figure of nearly 47 per cent. This global urban population reached 1 billion in 1960, 2 billion in 1985, and 3 billion in 2002. By 2030 it is expected to near 5 billion (UNDESA, 2006).