What term describes a merging of two or more metropolises with a population of 10 million or more?

The term that best describes the merging of two or more metropolises with a population of 10 million or more is "Megacity." This concept reflects not just the size of a city but also the interconnectedness and interdependence of urban areas. Megacities are characterized by their vast populations and can often result in the formation of larger urban agglomerations where economic, cultural, and social functions overlap, creating a complex metropolitan landscape.

Understanding megacities is crucial for urban planning and development, as these areas face unique challenges related to infrastructure, transportation, and public services due to their sheer scale and density. They exemplify how urban growth and development can create extensive metropolitan regions that are significant on a global scale.

Other terms like the "Threshold of Population" typically refer to the minimum population needed to support certain services or infrastructure, while "Highly Urbanized City" is more about cities that meet specific criteria for urban development and governance. "Urban Cluster" usually describes a collection of urban areas that may not reach the scale or characteristics associated with a megacity but are grouped based on proximity. Thus, "Megacity" accurately captures the essence of the merging large urban centers addressing those specific characteristics.