Today's lecture is about the mass {{U}}(1) {{/U}} of the world's population. There are two major {{U}}(2) {{/U}} why people are moving to cities. The first reason is {{U}}(3) {{/U}}. People are moving to the cities because that's where they can find {{U}}(4) {{/U}} and earn money. The second reason for the move to cities has to do with {{U}}(5) {{/U}} of life issues: comfort and {{U}}(6) {{/U}}. Cities often offer better {{U}}(7) {{/U}}. And then for many, city life is just more {{U}}(8) {{/U}}. An interesting consequence of urbanization is that the average {{U}}(9) {{/U}} of people in the countryside is increasing, while that of the cities is {{U}}(10) {{/U}}.
Three key {{U}}(11) {{/U}} can be identified in our cities. First of all, they're getting bigger. Most cities are bigger now than ever before. Cities are also changing shape. They're getting {{U}}(12) {{/U}} , because land is getting more and more expensive. {{U}}(13) {{/U}} have become a symbol of modern cities.
Cities are also changing shape in other ways. The {{U}}(14) {{/U}} Model and The {{U}}(15) {{/U}} Nuclei Model are probably more typical of the cities we know today. They show the urban {{U}}(16) {{/U}} that's occurring in contemporary cities.
The third change is that our cities are breaking up into {{U}}(17) {{/U}} communities, often by {{U}}(18) {{/U}} group or {{U}}(19) {{/U}} level. This often means that people stay within their community and do not come into contact with others from different {{U}}(20) {{/U}}.