Media release

From: Springer Nature

Urban growth: Cities now grow tall more than they sprawl

Cities may have expanded vertically more than they have horizontally since the 1990s, according to an analysis of three decades of satellite data from around the world published in Nature Cities.

Dense built environments characterise most cities today. Cities can grow by expanding outward, filling vacant urban land, or by expanding upward. This evolving structure affects how residents live, move and impact the broader environment. However, cities are large, varied, and constantly changing, so understanding broad trends is a challenge.

Steve Frolking and colleagues analysed satellite data from the 1990s through to the 2010s for more than 1,550 cities worldwide to characterize recent changes in urban growth. They combined two types of satellite data in their analysis: one that maps the footprint of cities from space in two dimensions and another that uses the reflections of beamed microwaves to characterize that footprint in three dimensions, allowing them to explore changes in the built environment. The authors found that over the past thirty years, cities have grown in distinct phases in line with their economic development. Since the 1990s, especially in rapidly developing world regions, cities have transitioned from low-rise, outward growth to more high-rise, upward growth. The authors note that this does vary by region: for example, in China, Southeast Asia and Africa, cities have expanded both up and out since the 2010s.

Frolking and colleagues conclude that their findings could aid our understanding of urbanization, especially as this process rewrites much of Earth’s surface.