By the end of 2008, for the first time in history, half of the world's population will live in urban centers, according to a revised United Nations population study. From VOA's New York Bureau, correspondent Barbara Schoetzau reports that the survey also predicts the world's urban population will almost double to 6.4 billion people by the year 2050.

The report's findings imply that urban areas must be prepared to absorb enormous numbers of people over the next four decades. U.N. population officials say the growth of cities will not only be caused by populations migrating from rural areas, but also by the transformation of many rural areas into urban centers.

Hania Zlotnik, the head of the U.N. Population Division, says most of the growth will be in small cities, not the mega cities like Tokyo, New York and Mexico City.

"By small cites, we mean cities with less than half a million people over time. I have to say for the cities that have more than half a million people, we know them by name and address," Zlotnik said. "But for the cities that have less than half a million people we really do not know where they are because they number in the tens of thousands. It is important to understand what you are going to have is birth of new cities. "

Most of the population growth is expected in less developed regions, especially Asia. Due largely to the rapid urbanization of China, Zlotnik says Asia is expected to become 50 percent urban within the next 15 years. Africa's urban population is expected to triple over the next three decades.

Zlotnik says urban centers are viewed as economically dynamic, attracting investment and creating employment. Ironically, improvements in rural areas can lead to population declines.

"Usually rural development implies having agricultural production that is more productive. To do that, you have to have less people producing because the productivity is measured on the basis of how much labor you put in. So you need to become more agribusiness and agribusiness uses less people. So they need to find employment for the excess labor that will be left when that happens," said Zlotnik.

The report represents the first time the United Nation has made urban projections as far ahead as the year 2050. The report is based on continued reductions in birth rates. If fertility rates remained at the current rate, the world population would reach eight billion by 2050.