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One challenge faced by researchers studying global urbanization is that different countries have different definitions of what constitutes an urban settlement. Many countries define urban settlements based on the number of people living in them. However, countries do not all use the same number; for example, Iceland uses a minimum population of 200, while Mali uses 30,000. Other countries use a combination of population and other factors, like the availability of planned public spaces. This variation makes it difficult for researchers to compare aspects of urbanization in different countries.

Urbanization is easily compared between countries when they have similar total populations.

Even though countries use different methods to define urban settlements, researchers consider any area having a population of at least 30,000 to be urban.

It is difficult for researchers to compare aspects of urbanization globally because of the various ways different countries define urban settlements.

Researchers focus on factors other than population when conducting studies on urbanization in Iceland.