Why the fastest-growing cities in the world are almost all in one region

In 1950, Lagos had roughly 300,000 people. The size of Omaha, Nebraska. A mid-century port city on the West African coast, colonial still, unremarkable in global terms. By 2025, depending on where you draw the boundary, it has somewhere between 17 and 21 million. One projection — from the Global Cities Institute, built on demographic trend extrapolation — puts it at 88 million by the end of this century. If that materializes, Lagos will be the largest city in the history of human civilization.

The first reaction is economic. Fast-growing cities mean booming economies — Shenzhen, Bangalore, Houston. The growth produces the wealth, the wealth produces the infrastructure, the infrastructure absorbs more people. That is the pattern most educated readers carry. It is not the pattern here.

What is driving Lagos — and Kinshasa, and Dar es Salaam, and thirty more cities across Sub-Saharan Africa — is not an economic boom. It is demography. And that distinction is everything.

The Scale

Lagos went from roughly 300,000 in 1950 to approximately 17.2 million in 2025 according to UN World Urbanization Prospects data — a 57-fold increase in one lifetime. The growth is not evenly distributed across those seven decades: the acceleration is itself accelerating.

Kinshasa, the capital of the Democratic Republic of Congo, now sits at roughly 17.8 million people and is growing at approximately 4.38% annually. That sounds like a percentage. It means around 774,000 new residents every year — roughly the entire population of a city the size of Amsterdam, arriving annually, permanently, requiring housing, water, food, sanitation, and some kind of economic activity that does not yet formally exist for most of them. Dar es Salaam, Tanzania’s commercial capital, is at approximately 8.6 million and growing at 4.91% annually, on a trajectory to cross 10 million before 2030. Luanda, the Angolan capital, stands at roughly 10 million.

These are not outliers within the region. Of 427 cities globally that grew faster than 4% in the decade through 2025, one-third were in Sub-Saharan Africa. One region. One-third of the world’s fastest-growing cities.

The Hoornweg & Pope projections

The figures for Lagos (88.3 million), Kinshasa (83.5 million), and Dar es Salaam (73.7 million) by 2100 come from Global Cities Institute Working Paper No. 4, by Daniel Hoornweg and Kevin Pope. They are built on trend extrapolation under sustained high-fertility assumptions — a single scenario, not a consensus forecast. Demographers note that SSA's fertility decline is accelerating faster than many 2010s models assumed, and that the projections do not incorporate the feedback loop by which urbanization itself tends to suppress fertility. These numbers represent a credible high-fertility scenario that describes where current trends lead if they persist, not a prediction that they will. Even if the actual figures land at half this scale, the structural argument — about demographic pressure, informal urbanism, and fiscal incapacity — is fully intact.

The historical context requires precision. Shenzhen, China’s manufacturing metropolis, grew from roughly 30,000 city-proper residents in 1980 to approximately 12–13 million by 2020 — a transformation of comparable visual drama. Chicago in its fastest decades grew at annualized rates exceeding 10% — from 4,470 in 1840 to nearly 30,000 in 1850, 112,000 in 1860, 299,000 in 1870. Both cases were spectacular. Neither is analogous.

Shenzhen’s growth was the product of deliberate industrial policy — the state designated it China’s first Special Economic Zone, built infrastructure ahead of population, and directed export manufacturing into it. The city grew because factories needed workers. Chicago’s explosive decades coincided exactly with the expansion of the railroads, the stockyards, the grain trade, the steel mills: every person who arrived had somewhere to go that paid them. The city grew because an industrializing economy was generating demand for labor faster than it could be supplied.

What is happening in Sub-Saharan Africa’s fastest-growing cities is mechanistically different. There is no equivalent industrial engine, no deliberate policy reorientation toward labor-absorbing manufacturing, no state-directed infrastructure construction racing ahead of the population wave. The cities are growing because people are going to them. Not because economic demand is pulling them — because demographic pressure is pushing them, and cities are where people go when there is nowhere else.

It is the structural fact from which everything else in this story follows.

The Demographic Engine

Sub-Saharan Africa’s total fertility rate in 2024 was 4.34, according to World Bank data. The global replacement rate is 2.1 — the level at which, over time, a population neither grows nor shrinks. SSA’s average is more than double that. Nigeria’s TFR is between 4.48 and 4.8, according to the 2023–24 Demographic and Health Survey. The DRC’s is 6.05.

These are not anomalies within a broader global trend. They are Sub-Saharan Africa’s defining demographic position. Every other major world region — East Asia, South Asia, Latin America, the Middle East — has either completed the demographic transition or is well into it. South Korea’s TFR is below 0.8. Brazil is below replacement. Even India crossed below 2.1 in recent years. Sub-Saharan Africa, as a region, has not. It is the only major world region that has not.

A high TFR produces a young, rapidly growing population — more children than adults, more adults tomorrow than today. In SSA, the rural economies that this population is born into are predominantly smallholder agricultural, with limited capacity for productivity growth under land pressure. They cannot absorb additional labor at the rates being generated. Young people move. The direction is cities — not because formal employment is waiting, not because there are factories and offices and service industries hiring at scale, but because cities offer density, proximity, informal economic possibility, networks that rural areas cannot provide. The migration is rational. The destination is not an economic boom. It is simply the place with the best available odds.

Contrast this explicitly with the 19th-century factory pull that underpins most Western intuitions about urbanization. Manchester, Chicago, Pittsburgh — people moved to these cities because the industrial economy was generating more formal employment than existed rural workers to fill it. The city grew because the economy needed it to. In SSA today, the relationship is inverted. The population is growing faster than any economy is generating demand for labor, formal or informal. The city grows not because it is ready to receive people but because it has no mechanism to refuse them.

The pattern is common to Lagos, Kinshasa, Dar es Salaam, and dozens of smaller SSA cities — but it is not identical in character. Kinshasa’s growth includes a significant displaced-population component: conflict in the Kivu region of eastern DRC has driven sustained movement toward the capital, meaning some of its growth represents flight rather than simply demographic pressure. Luanda’s expansion has been shaped partly by Angola’s oil revenues and the construction phase they funded. These are local modifiers. They add to the demographic pressure or alter its character in specific cases. They don’t substitute for it.

The aggregate consequence: SSA’s urban population is projected to increase from approximately 574.7 million in 2025 to approximately 1.26 billion by 2050, according to UN World Urbanization Prospects 2025 data — a near-doubling in 25 years. The all-Africa figure, covering all 54 African countries, is closer to 1.4 billion (OECD/AfDB Africa Urbanisation Dynamics 2025); these are different geographic scopes and must not be conflated. Even under the most optimistic fertility-decline scenarios, the trajectory is essentially locked in by the age structure already built into SSA’s population.

The fertility decline debate

Some demographers argue SSA's fertility is declining faster than standard models project — female education uptake is accelerating, contraceptive adoption is increasing in parts of West Africa, and urbanization itself tends to suppress fertility. Adhikari et al., "Forecasting Africa's fertility decline by female education groups" (PNAS, 2024; doi: 10.1073/pnas.2320247121) projects faster decline under high-education scenarios. This matters: it means the highest-end population projections — including Hoornweg and Pope's 2100 figures — are likely overestimates. But the demographic math for the next 25 years is largely insensitive to which fertility trajectory materializes from here. The population already born — the children, adolescents, and young adults who will move to cities between now and 2050 — is already counted. Population momentum is not sensitive to what fertility does in 2030. The near-doubling of SSA's urban population by 2050 is locked in across all plausible scenarios. Fertility decline changes the century's second half, not its first.

What the City Actually Is

The city most people picture when they hear about millions of people arriving annually has streets, buildings with addresses, pipes that bring water. A municipal government that issues permits, collects rubbish, installs streetlights. A formal labor market — or at least an informal one operating in the shadow of a formal one. That city exists in many places. It is not the one being described here.

Fifty-five to sixty percent of Sub-Saharan Africa’s urban population lives in informal settlements, according to UN SDG monitoring data — areas with no legal land tenure, no registered addresses, limited or no connection to piped water, electricity, or sewage systems. The UN SDG Report 2019 counted approximately 238 million people in SSA in slum conditions as of that year. The numbers have grown since.

In 2025, Bettencourt and Marchio published a landmark paper in Nature (vol. 645, pp. 399–406) mapping every street block in Sub-Saharan Africa using high-resolution satellite building footprint data. The paper found that more than 500 million people in the region live in what it classifies as “high-complexity” urban areas: neighborhoods with limited piped services, no legal addresses, and no emergency vehicle access. These are not peripheral anomalies on the edges of otherwise functional cities. In Kinshasa, Dar es Salaam, and across Lagos’s sprawling northern and eastern neighborhoods, informal settlement is the dominant form. The formal city — the city of addresses, permits, and pipe networks — is the exception, not the rule.

The informal economy follows the same logic. World Bank Policy Research Working Paper 10703 (“Urban Informality in Sub-Saharan Africa,” 2024) estimates that 56–65% of SSA urban workers are informal — no contract, no registration, no payroll taxes, no social protections. The lower bound of this range is 56.3%; the upper is 64.6%. When Nigeria is excluded from the sample, the figure rises to approximately 70%. The ILO, using broader definitional and geographic coverage, estimated in 2018 that 76.3% of Africa’s urban employment was informal. The methodologies differ; the structural conclusion across all approaches is consistent.

This is not a survival economy operating in the shadow of a real economy. It is the economy.

The street markets, the small-scale manufacturers, the transport operators, the mobile money agents, the urban farmers — these are not anomalies or failures. They are the primary economic institution of SSA urban life. They generate income, allocate resources, discipline prices, and perform social functions that formal markets perform elsewhere. The vocabulary of the informal sector — the implication that there is a formal sector it is informal relative to — consistently misleads.

Dar es Salaam makes the urban agriculture point with particular clarity. Research by Malekela and Nyomora found that approximately 47% of food products in surveyed local markets are sourced from urban and peri-urban agriculture, rising to 60–80% for fresh vegetables. A 2024 Tandfonline study (“Going with the food flow”) found that 70% of the city’s amaranth — a staple green leafy vegetable — is produced within city limits. This is not hobby farming. It is a functional adaptation to the absence of reliable cold-chain logistics and formal distribution networks. The city feeds itself, at significant scale, through a food system the formal economy did not build and formal planners did not design.

Informal settlement means inadequate sanitation, elevated disease burden, vulnerability to fire and flood, absence of the legal protections that formal tenure provides. Informal employment means no safety net, no sick leave, no pension, extreme volatility. Urban farming works, but it also carries risks — contaminated soil, water scarcity, land insecurity. These systems are not fine. But they are the systems that exist; they emerged because formal alternatives were never built at required scale, and they work — imperfectly, unequally, with significant human cost — in the absence of anything else. The world has limited tools to evaluate them, because every tool built for urban analysis was built for the other kind of city.

The Governance Gap

Who governs this, and how?

The Economic Commission for Africa, reporting through Africa Renewal in January 2025, assessed six major African cities — Addis Ababa, Dar es Salaam, Kigali, Lusaka, Nairobi, and Yaoundé — and found them functioning below 40% of their economic capacity. The specific framing was about the gap between what municipal governments could potentially generate in local revenue and what they actually collect. Most SSA city governments are structurally dependent on central government transfers — funding that is politically determined, inconsistently disbursed, and not indexed to the pace of urban growth. A city growing at 4–5% annually cannot wait for a government budget cycle to catch up.

Lagos Water Corporation has an installed capacity of approximately 210 million gallons per day. The city’s demand, on current population projections, is in the range of 780 million gallons per day — a figure from the Lagos State Masterplan that expired in 2020, based on projected 2025 population reaching 32 million. Five years after the Masterplan’s expiry, the LWC’s capacity has not substantially increased. Government pipelines reach approximately 35% of Lagos’s population. The remaining 65% — millions of people — source water from tanker trucks, private boreholes, sachet water sold from carts, or open sources. Each of these is more expensive per unit than piped water, which means the poorest households in Lagos pay more for water than the wealthiest ones. That inversion is not unusual in cities where formal infrastructure covers less than half the population. It is the standard outcome.

In 2024, Lagos was the epicenter of Nigeria’s cholera outbreak. National data from the Nigeria Centre for Disease Control and Prevention (NCDC) showed 4,809 suspected cases and 156 deaths nationally through epidemiological week 29 (July 15–21, 2024). At the outbreak’s peak, Lagos accounted for approximately 65% of national cases. Cholera is a waterborne disease. Its concentration in Lagos is a direct consequence of the water access gap.

Kinshasa’s situation is structurally comparable. Approximately 52% of the DRC’s population has access to an improved water source; 29% to improved sanitation, according to UNICEF DRC data. The city’s water utility, REGIDESO, operates infrastructure chronically degraded by power failures — Kinshasa, home to roughly 18 million people, relies substantially on biomass for energy. A city the size of metropolitan New York, running on charcoal and wood.

What matters most — and what the standard development-aid framing consistently misses — is that this is not principally a resource problem. It is a structural one.

The primary fiscal mechanisms for urban infrastructure investment — property taxes, formal-economy income taxes, development fees, bonds backed by future revenue streams — all presuppose a substantial formal economy and a formal property market. Property taxes require that properties be registered, assessed, and legally owned. Income taxes require that income flows through traceable formal employment. Development fees require that construction happens through permitted processes. When the majority of employment is informal — World Bank WPS 10703 (2024) puts it at 56–65%, rising to 70% when Nigeria is excluded — and most residential settlement is unregistered, these fiscal instruments do not function. Not because governments are incompetent or corrupt (though both of these things occur). But because the instruments themselves presuppose a city structure that does not exist.

More aid patches specific shortfalls. It funds a water treatment plant, replaces a section of pipe, trains municipal planners. What it cannot do is rebuild the fiscal architecture. Because the fiscal architecture’s dysfunction is not a resource problem — it is a consequence of how this city formed in the first place. Informal, rapid, driven by demographic pressure rather than economic development. The city that emerged from that process is not a failed version of the formal city. It is a different kind of city that the governance instruments available to it were not designed to manage.

This is not a criticism of African governance. It is a structural observation about what happens when a particular form of urbanization — demographically driven, economically informal, operating at enormous pace and scale — meets institutional instruments designed for a different form.

What This Means for the Century

By 2050, Sub-Saharan Africa’s urban population will reach approximately 1.26 billion. That is 25 years from now. Within a single generation, a very large share of all new urban humanity will be in cities built on informal settlement, governed by municipalities that cannot raise revenue at the pace of growth, and organized primarily around informal economic relationships.

The governance infrastructure required to deliver what urban civilization is assumed to provide — epidemic response, mass education, piped water, climate adaptation — is not a set of separable programs. It is a single underlying substrate: a government that knows who lives where, can tax what they earn, and can borrow against what it will collect. That substrate requires registered addresses, traceable income, permitted construction. It requires the other kind of city. None of it has been built here, and none of it is being built at anywhere near the pace required.

That is not pessimism. It is description. The institutions nominally tasked with managing this — the UN system, bilateral development agencies, national governments, municipal planners — are operating with frameworks built for the other kind of city, at a pace that is not remotely commensurate with the speed of growth.

Mobile money has transformed informal financial systems across East Africa: Kenya’s mobile money penetration reached 91% in mid-2025 and approached 98% by year-end, according to Communications Authority of Kenya sector data and fintech reporting, with Safaricom’s M-Pesa holding roughly 89% of the market. Community-level water systems in Lagos’s peri-urban areas reach where the LWC cannot. Urban food systems in Dar es Salaam function at city scale. None of this is trivial. But none of it scales — not to the epidemic response, the education, the drainage, the climate adaptation that a city of 30 or 50 million requires. The failure modes, when dense informal settlement meets epidemic disease or flood, are severe and not buffered by a government with the capacity to respond.

The assumptions embedded in what we call urban civilization — about what a city can and should provide, what governance capacity it requires, what scale of infrastructure it depends on — were built on one mode of urban growth. Economically driven. Institutionally formal. Supported by states with the fiscal capacity and planning apparatus to anticipate growth rather than perpetually chase it. That mode produced the cities most people in wealthy countries live in, and the conceptual frameworks used to evaluate every other city in the world.

The mode that will dominate this century is a different one. Not as an exception. As the norm.

クロージング

Lagos went from 300,000 to 17 million in one human lifetime. No previous city did it without an industrial economy pulling people in, or a state with capacity to build ahead of them.

More infrastructure investment would help — no one disputes it. The question the growth raises is what the world looks like when the fastest-growing cities, housing the majority of future urban humanity, are the ones the world’s institutional architecture is least equipped to understand, manage, or plan for. Not historically. Not in the next decade. Not as a temporary condition on the way to something more familiar. As the durable condition.

The 21st-century city is being built right now. At 4.38% annually in Kinshasa. At 4.91% in Dar es Salaam. Largely outside formal systems, largely outside the planning frameworks, largely outside the attention of institutions that claim to be managing it. The people doing the building — with their hands, their informal networks, their urban farms and mobile money transactions — are not operating inside frameworks designed for them, because no such frameworks exist at the required scale. The institutions nominally responsible are managing the legacy city, not the one currently being built. There is no mechanism in view that changes this at the pace the growth demands.

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主な情報源と参考文献

UN Population Division, World Urbanization Prospects 2025. population.un.org/wup/

Hoornweg, D. & Pope, K. “Population predictions for the world’s largest cities in the 21st century.” Global Cities Institute Working Paper No. 4; published in Environment and Urbanization, vol. 29, no. 1, pp. 195–216, 2017. doi: 10.1177/0956247816663557. Population projection data: sites.ontariotechu.ca/sustainabilitytoday/urban-and-energy-systems/Worlds-largest-cities/population-projections/

Adhikari, S. et al. (incl. Vollset, S.E.). “Forecasting Africa’s fertility decline by female education groups.” Proceedings of the National Academy of Sciences, vol. 121, no. 46 (2024). doi: 10.1073/pnas.2320247121

Bettencourt, L.M.A. & Marchio, N. “Infrastructure deficits and informal settlements in sub-Saharan Africa.” Nature, vol. 645, pp. 399–406 (2025). nature.com/articles/s41586-025-09465-2 Interactive data: millionneighborhoods.africa

World Bank Policy Research Working Paper 10703. “Urban Informality in Sub-Saharan Africa: Profiling Workers and Firms in an Urban Context.” 2024. openknowledge.worldbank.org

Nigeria Demographic and Health Survey 2023–24. DHS Programme, Report PR157. dhsprogram.com

World Bank. “Fertility rate, total (births per woman) — Sub-Saharan Africa.” data.worldbank.org/indicator/SP.DYN.TFRT.IN?locations=ZG

World Bank. “Fertility rate, total (births per woman) — Congo, Dem. Rep.” World Bank Open Data, 2023.

International Labour Organization. “Women and Men in the Informal Economy: A Statistical Picture.” ILO, 2018. ilo.org

UN SDG Report 2019. Tracking progress toward UN Sustainable Development Goals, Goal 11. unstats.un.org/sdgs

Wessels, M.T. & Hemerijckx, L.-M. “Going with the food flow: The contribution of urban agriculture to a growing African city.” Development Southern Africa, 2024. doi: 10.1080/0376835X.2024.2398547

Malekela, A.A. & Nyomora, A. “Food security: The role of urban and peri-urban agriculture. A case of Dar es Salaam City, Tanzania.” International Journal of Agronomy and Agricultural Research, vol. 13, no. 2, pp. 50–62, 2018. innspub.net/food-security-the-role-of-urban-and-peri-urban-agriculture-a-case-of-dar-es-salaam-city-tanzania/

UNECA / Africa Renewal. “Unlocking municipal finance for sustainable urban services and SDG success in Africa.” Africa Renewal, January 2025. africarenewal.un.org/en/magazine/unlocking-municipal-finance-sustainable-urban-services-and-sdg-success-africa

CAPPA Africa / Guardian Nigeria. “Five years after masterplan expired, Lagos still in search of safe drinking water.” cappaafrica.org/2025/08/30, guardian.ng

Nigeria Centre for Disease Control and Prevention. Cholera Situation Report, Epidemiological Week 29 (July 15–21, 2024). ncdc.gov.ng/diseases/sitreps. Also available via ReliefWeb.

UNICEF Democratic Republic of Congo. Water, Sanitation and Hygiene. unicef.org/drcongo/en/what-we-do/water-sanitation-and-hygiene

World Bank. “Supporting drinking water access, a key to progress in DRC.” November 2023. worldbank.org

Communications Authority of Kenya. ICT Sector Statistics Report, Q2 2025–26 (October–December 2025). ca.go.ke

FinTech Magazine / Techweez. “Kenya’s Mobile Money Penetration Reaches 91%.” fintechmagazine.africa/2025/09/26; “Kenya Adds 2.7 Million Mobile Money Users in 3 Months to Hit 98% Penetration.” techweez.com/2026/04/07

OECD/AfDB. Africa Urbanisation Dynamics 2025. oecd.org

Macrotrends. “Lagos, Nigeria Metro Area Population 1950–2025.” macrotrends.net

Macrotrends. “Kinshasa, DRC Metro Area Population 1950–2025.” macrotrends.net

Macrotrends. “Dar es Salaam, Tanzania Metro Area Population 1950–2025.” macrotrends.net

Macrotrends. “Luanda, Angola Metro Area Population 1950–2025.” macrotrends.net

US Bureau of the Census. Historical population data for Chicago, Illinois, 1840–1900. biggestuscities.com/city/chicago-illinois; physics.bu.edu/~redner/projects/population/cities/chicago.html