Final answer:
The structure of underground cities and their evolution are key components of urban geography, influenced by theories such as Central Place Theory and shaped by elements like urban planning and transportation networks.
Step-by-step explanation:
The structure of underground cities that power our world can be described through the lens of urban geography. Walter Christaller's Central Place Theory provides a framework to understand the pattern of urbanization and the spatial distribution of cities, towns, and villages. This theory is vital to comprehend how urban centers evolve and how they are structured in terms of offering goods and services to their hinterlands. It indicates how settlements of different sizes are distributed in a manner that allows them to be most accessible to the population.
Aspects like the elevated and subterranean railroads ('el' or the 'subway') and urban planning are fundamental components of underground cities. These transportation networks facilitate the division of urban spaces into distinct districts, catering to different needs such as manufacturing, finance, shopping, and residential purposes. Furthermore, historical examples like Uruk in Mesopotamia or Monte Albán in Mesoamerica showcase the significance of urbanization to the modern world, illustrating patterns like proximity to waterways and the emergence of administrative capitals based on agricultural surplus.