The planet is becoming a world of cities, as the twentieth century witnessed a remarkable development of cities, both in terms of numbers and size (Scoru, 1993). At the beginning of the nineteenth century, about three percent of the world's population lived in urban areas. At the beginning of the 20th century, this number reached about 15%, reaching 46% in the late 20th century. In 2000, this increased to 48.2%. Studies show that in 2025, it will reach 62.5%. On this basis, about two thirds of the world's population will by then live in cities (Bradshaw, 1987)
A look at the trend of population growth in developing countries is far more worrying than the whole world. For example, in 1960, the share of these countries in the number of metropolitan cities in the world was 9 out of 19 urban areas, while in 2000, this number reached 50 metropolitan areas out of a total of 66 mother cities (Lo, Fu-Chen 2001). However, there are many differences between the third world and the whole world (in particular in developed countries) in terms of the factors that make up urbanization and the consequences this process brings about (Roberts, 1978). The differences in levels of urbanization and growth rate in these two systems reveal the differences in the socioeconomic systems that are rooted in historical, cultural and other processes. In wealthy countries, urban structures are clearly defined. Population growth is minimal and urban migration process is negligible. But for a developing country, applying this city vision and optimistic assessment will be misleading.
As it was stated, the earth was for tens of thousands of years empty of any building made by human hands. These settlements gradually became more compact, turned into villages and then towns. Since the last few centuries, cities have become very complex human settlements. Despite the fact that the city has a relatively long history, but widespread urbanization has a history shorter than 200 years.