The physical features of the world's largest cities are shifting as urban centres in Asia expand upwards and outwards.
Steve Frolking at the University of New Hampshire in Durham and his colleagues combined satellite observations of night-time illumination and urban backscatter — the reflection of microwaves from the surface of built-up land — to infer how the structure of 100 large cities around the world changed from 1999 to 2009. Most Chinese cities grew vertically, echoing drastic increases in land prices. However, cities in India and Africa expanded outwards, owing to factors such as unplanned urban development and building-height limits.
The data could be used to help researchers to understand how urbanization affects energy consumption and greenhouse-gas emissions, the authors note.