A recent article in Place—an urban journalism initiative from the Thomson Reuters Foundation—highlights the problems with the United Nations' projections of global urban populations. The article also looks at the efforts of independent research efforts from the European Commission and Professor Shlomo Angel's NYU Urban Expansion initiative to improve the accuracy of global urban popualtion counts. The trouble with the UN projections arises:
...because countries self-report their demographic statistics to the U.N. and they use widely different standards.
For example, India defines a city as a place where at least 75 percent of males are not working in the agricultural sector.
China provides an official number of cities, although its rapid growth suggests a different picture on the ground.
Researchers at the New York University Urban Expansion Project, who have also developed a satellite-based definition of cities similar to the European Commission's, calculate 387 cities of more than 100,000 people are not officially classified as such by the Chinese government.
"The city in China is a very political idea," NYU researcher Patrick Lamson-Hall told the Thomson Reuters Foundation.
Most countries use a population density threshold, but those figures can vary widely.
The United States, for example, starts classifying settlements as urban when they exceed a population threshold of 2,500.
For Egypt, the number is 100,000, according to Dijkstra.
"The numbers released by the U.N. are accurate in that they report what the countries tell them, but as far as being able to make comparisons between countries go, they are not usable," Lamson-Hall said. "It’s beyond apples and oranges."