What constitutes a "megacity"?

A "megacity" is defined as an urban area that has a population exceeding 10 million people. This criterion is widely used by demographers and urban planners to categorize and analyze the size and growth of cities on a global scale. The definition emphasizes not just the concept of a large city, but one that surpasses a significant threshold of population, highlighting the considerable urbanization and associated challenges that come with such large population densities, including infrastructure, housing, transportation, and environmental concerns.

In contrast, the other options do not fit the established definition of a megacity. For instance, a population over 5 million, while indicative of a large urban area, does not meet the specific threshold that classifies a city as a megacity. Similarly, merely having extensive metropolitan areas does not provide a clear measure of population. Lastly, local governments with diverse regions may not refer specifically to population size at all, thus not aligning with the established criteria for classifying megacities.