Global Urban Structure Reshaping: Paradigm Shift from Sprawl to Vertical Concentration

The evolution of global urban forms is never just about simple geographical area expansion. In recent years, monitoring over more than 1550 cities globally using advanced remote sensing technology has revealed a profound, structural paradigm shift: the driving force behind urban growth is shifting from traditional "lateral spreading out" to the more challenging "vertical building up." This transformation signifies a fundamental restructuring of global urban civilization in terms of spatial organization and material form.

Past research often simplified urban expansion to the spreading and filling of land, i.e., a two-dimensional (2D) growth pattern. However, new three-dimensional (3D) monitoring methods, especially those utilizing microwave backscatter data, are beginning to reveal more complex, three-dimensional growth mechanisms within cities. Research indicates that over the past thirty years, while the building coverage of cities in many regions has increased, their growth rate has significantly slowed, whereas the growth rate of building volume—the growth in the vertical dimension—has been continuously climbing in almost all areas and cities. This divergence between "area expansion" and "height growth" is a key signal of a fundamental change in the global urban structure.

This transition from "spreading out" to "building up" is not a uniform global phenomenon; it exhibits regional differences and phase characteristics. In some areas, cities may still rely on low-density, horizontal expansion models; in others, particularly in the rapid development of Asia, the driving force of vertical growth is even stronger. This trend toward verticalization has far-reaching structural consequences. It means that the demand for building materials and energy will undergo a qualitative change, the traditional logic of low-density, low-density resource allocation will become obsolete, replaced by structural requirements for higher density and more efficient spatial utilization.

From the perspective of urban climate and environmental impact, this verticalization is a potential new direction for climate adaptation strategies. The impact of the three-dimensional urban structure on local microclimates (such as the urban heat island effect) is far more complex than planar expansion; changes in vertical form directly affect ventilation, shading, and heat exchange patterns between building clusters. Therefore, studying the dynamic relationship between the three-dimensional urban structure and climate is becoming a core issue for understanding future urban resilience and sustainability.

However, although the scientific community has begun to capture this trend, precisely quantifying and long-term tracking this global dynamic of vertical growth still faces challenges in data acquisition and methodology. Currently, obtaining high-precision, long-term three-dimensional urban form data remains a bottleneck for research. Future urban strategy formulation will no longer just focus on "where cities should expand," but rather on "how cities should grow upward"—this requires urban governors and planners to leap from a two-dimensional land-use mindset to a three-dimensional spatial form management mindset.The focus of global urban competition is shifting from who can occupy more peripheral land to who can more effectively manage and optimize its internal vertical space. This is not just a competition at the technical and engineering level, but a profound civilizational game involving resource allocation, environmental carrying capacity, and social equity. Against the backdrop of globalization's restructuring, how cities navigate this vertically driven new structure will determine their survival form and role in the post-industrial era.