GLOBAL - The Indonesian capital of Jakarta is now the world’s most populous city, home to an estimated 41.9 million people, according to a landmark report from the United Nations. The finding, part of the UN Department of Economic and Social Affairs' (UN DESA) "World Urbanisation Prospects 2025" report, sees Tokyo slip to third place with 33.4 million residents, behind Dhaka, Bangladesh, at 36.6 million. This significant reordering of global urban rankings stems not from a sudden population boom, but from a new, more accurate methodology that provides crucial insights into the scale of global urbanisation—a trend with profound implications for East Africa’s rapidly expanding cities.

The re-ranking is the result of the UN's adoption of a globally standardised method to define urban areas, known as the 'Degree of Urbanisation' (DEGURBA). Previously, population counts relied on varying national definitions of a "city," which often made direct comparisons inconsistent. The new assessment uses satellite imagery and population density data to create a more comparable international standard. Patrick Gerland, Chief of the Population Estimates and Projections Section at the UN Population Division, stated that the new assessment “provides a more internationally comparable delimitation of the urban extent based on similar population and geospatial criteria.”

A Planet of Cities

The report underscores a dramatic global shift. In 1950, only 20% of the world's 2.5 billion people lived in cities. By 2025, cities are home to 45% of the planet's 8.2 billion people. The number of megacities—urban areas with over 10 million inhabitants—has surged from just eight in 1975 to 33 in 2025, with the majority located in Asia. This relentless trend is set to continue, with the UN projecting that two-thirds of all global population growth by 2050 will occur in urban centres.

Jakarta: A Case Study in Urban Stress

Jakarta's new status as the world's largest metropolis highlights the severe pressures that accompany hyper-urbanisation. The city's explosive growth is a magnet for economic opportunity, but it has also led to profound infrastructural and environmental crises. Jakarta is frequently cited as one of the world's most congested cities, and it faces an existential threat from land subsidence, caused primarily by the excessive extraction of groundwater. Some parts of the city are sinking by as much as 25 centimetres per year, with projections indicating that large areas of North Jakarta could be submerged by 2050. This environmental crisis, coupled with challenges in housing and pollution, has prompted the Indonesian government to initiate the ambitious, multi-billion-dollar project of relocating its capital to a new purpose-built city, Nusantara, in Borneo.

Lessons for Nairobi and East Africa

While geographically distant, Jakarta's challenges offer a critical cautionary tale for Nairobi and other fast-growing East African cities. Africa has the highest urban growth rate in the world, and like Asia, is urbanising rapidly. The population of Nairobi's metropolitan area is estimated at 5.77 million in 2025 and is projected to exceed 7 million by 2030. According to UN-Habitat, Kenya's overall urban population is expected to constitute more than half the national total by 2050.

This rapid growth already strains Nairobi's infrastructure, evident in traffic congestion, housing shortages, and pressure on essential services like water and sanitation. The experiences of Asian megacities provide vital lessons. Analysts stress that for urbanisation to be a sustainable driver of economic growth, it must be accompanied by strategic, long-term planning and massive investment in public infrastructure. Key policy areas for Kenyan national and county governments include developing robust public transport networks, promoting affordable housing to prevent the expansion of informal settlements, and ensuring environmental sustainability is at the core of urban planning.

The UN's recalibration of urban populations is more than a statistical update; it is a clear signal of a global demographic shift. For Kenya, Jakarta's story is a glimpse into a possible future, underscoring the urgent need to build resilient, inclusive, and sustainable cities capable of managing the immense pressures of 21st-century urban growth.