Abstract
Urbanization has surged
over the past decades. Global major cities’ land urbanization and
population urbanization have intensifying pressures on urban
climate, public health, and energy consumption. A favorable vision
for assessing urban habitats’ living conditions necessitates
recognizing the evolution and current status of major global
cities’ three-dimensional structure and spatiotemporal
trajectories. However, a lack of high-resolution, long-term data
hinders obtaining metrics reflecting living conditions. This study
addresses this gap by generating a 30-meter resolution
spatiotemporal three-dimensional urban expansion dataset for 2071
global major cities (1990–2020). Integrated with socioeconomic
data, it reveals adherence to Zipf's Law, reflecting pronounced
unequal development and a global-scale Matthew effect. Most cities
fell within the 0–1 km³ volume range, with 12 cities and 41 cities’
volume > 9 km³ in 1990 and 2020, respectively. About two-thirds
of major cities experienced building expansion rates exceeding
population growth rates between 2000 and 2020. Per capita building
volume correlates with the GDP. Africa is the only continent to
witness a decline in per capita building volume over the past 20
years, indicating a further decline in the living conditions of
urban residents. Focusing on internal building structures, an
inequality index characterizes height diversity within cities.
Asian cities exhibit the highest global inequality index, marked by
supertall building additions. This study not only compares major
cities' overall size and growth patterns in three dimensions but
also analyzes the distribution of building heights within each city
in detail. The findings contribute to identifying and addressing
urbanization challenges, supporting habitat environmental
assessments, and measuring progress toward sustainable goals.