The population explosion is taking place in all the world. And, most of the big cities are overpopulated. most of the questions have been giving a problem. For example, why do people still move to big cities? or what do you go to the city ? and more and have a lot of the reasons have been giving explanation. However, i thing two reasons is big about: The first, the city where have favorable, it have a flat road, weather is very good, or a school, a hospital, a bank, a park and more, everything is very favorable. So, it's one in two reasons. Nowaday, the poeple have the trend enjoys life because the their life is becoming full, they aren't focus a lot of make money, so they care for health and spirit more than. For example, a people sicks, you needs hospital but that contryside don't hospital, so you go to city where have hospital, but when you going to hospital, you sicks seriously. The second, the most important reason is the problem of job. It's problem of a person that is problem of the world. In the city, the people can look for good job or the job accordants with degree. And, salary in the city higher than salary in the countryside. For example, a peole lived countryside, each of month you could look for one million vietnam dong, but you went to the city, you can look for three million vienam dong. We can see, that example proves about why most of the big cities are overpopulated