Foundationsdevelopment
Urbanization: The Economics of Cities
Overview
Over half of humanity now lives in cities; by 2050 it will be two-thirds. Urbanization is development's most visible face — and its most powerful engine: cities concentrate workers, firms, and ideas, raising productivity through agglomeration. But rapid urbanization also produces slums, congestion, and pollution. This lesson explains the rural-urban migration decision (Harris-Todaro), agglomeration economies, the informal settlements challenge, and what makes cities work.
Learning objectives
- Explain the Harris-Todaro migration model
- Describe agglomeration economies: sharing, matching, learning
- Analyze slums: causes, economics, and upgrading vs. clearance
- Evaluate urban costs: congestion, pollution, housing
- Identify policies for productive, livable cities
Why people move: Harris-Todaro
The Harris-Todaro model (1970) explains a puzzle: migrants flood cities despite visible urban unemployment. The answer: they respond to expected income — the urban wage times the probability of getting a job — not the guaranteed wage. If city wages are triple rural incomes, migration continues even with 30% unemployment, because the expected gain still exceeds rural earnings. The model predicts equilibrium urban unemployment as the mechanism that equalizes expected incomes. Policy implication: creating urban jobs can paradoxically increase unemployment by attracting more migrants — the 'Todaro paradox' that humbled many job-creation schemes.
Migrants gamble on the city: high wages × job probability vs. certain rural poverty. Urban unemployment is the equilibrating mechanism, not a policy failure per se.
Agglomeration: why cities are productive
Firms and workers cluster because of three Marshallian forces. Sharing: common infrastructure, suppliers, and labor pools (Shenzhen's electronics ecosystem). Matching: thick labor markets pair specialized workers with specialized firms — the economist finds her niche only in a big city. Learning: ideas spill over through face-to-face contact — the café, the conference, the job-hop. Empirical estimates: doubling city size raises productivity 2–8%. This is why economists favor urbanization despite its messiness — density is a productivity technology, and restricting it (through bad zoning or rural romanticism) has real GDP costs.
Across countries and eras, the elasticity of productivity with respect to city size centers around 0.05: double the city, gain ~5% productivity. Compounds powerfully over decades.
Slums: the shadow of urbanization
A billion people live in slums — informal settlements lacking secure tenure, water, sanitation, or durable housing. The economics: slums are the market's answer to unaffordable formal housing near jobs; residents trade housing quality for location and livelihood. Forced clearance destroys social networks and livelihoods without solving the affordability gap — the evidence favors in-situ upgrading (water, sanitation, tenure regularization, as in Mumbai's and Nairobi's programs). Over time, today's slums often become tomorrow's working-class neighborhoods (much of Seoul and Singapore started as such). The policy goal is upgrading pathways, not eradication fantasies.
Hernando de Soto estimated the poor hold trillions in 'dead capital' — untitled homes and businesses that can't collateralize loans. Titling unlocks this, though the credit effects proved smaller than hoped.
The costs: congestion, pollution, prices
Agglomeration's downsides are real. Congestion: traffic, crowded transit — time losses that can erase productivity gains (Jakarta, Lagos). Pollution: density concentrates emissions; Delhi's air is among the world's deadliest. Housing: successful cities price out workers — the 'superstar city' affordability crisis from San Francisco to Mumbai. And inequality: urban premiums accrue to the skilled while the unskilled face slum rents. Congestion pricing (London, Singapore, Stockholm), mass transit investment, and upzoning near jobs are the economist-approved responses — pricing the externalities rather than fighting density itself.
Congestion charges, pollution taxes, and land-value capture let cities keep agglomeration's gains while curbing its costs — fighting density itself sacrifices the gains.
Making cities work: the policy frontier
What separates functional from failing cities? Land use: flexible zoning and floor-area ratios let supply meet demand (Houston's laxity vs. Mumbai's strangulation). Transport: bus rapid transit (Bogotá's TransMilenio) delivers metro-like capacity at bus costs. Governance: metropolitan coordination across fragmented municipalities (the killer of many African and Latin American cities). Finance: property taxes and land-value capture fund infrastructure from the value it creates. And realism: plan for the urbanization that's coming — serviced land and trunk infrastructure ahead of settlement beats retrofitting slums later. The developing world's urban century will be won or lost on these unglamorous fundamentals.
Key points
- Rural-urban migration follows expected income (Harris-Todaro) — urban unemployment equilibrates the flow.
- Agglomeration (sharing, matching, learning) makes cities 2–8% more productive per doubling of size.
- Slums are affordable-housing markets near jobs; upgrading beats clearance.
- Congestion, pollution, and housing costs are the real urban challenges — priced, not wished away.
- Zoning reform, BRT transit, metro governance, and land-value finance make cities work.
Common misconceptions
✓ Truth: Slum residence is a rational trade: housing quality sacrificed for job access. Migrants correctly judge that city expected incomes beat rural certainty — the model predicts exactly this.
✓ Truth: Clearance destroys livelihoods and networks without fixing affordability; residents rebuild elsewhere. In-situ upgrading (water, tenure, sanitation) has the evidence on its side.
✓ Truth: Dense cities are greener per capita (less driving, shared heating, smaller homes). The environmental problem is unmanaged sprawl and dirty energy, not density itself.
Practice questions
Q1. The Harris-Todaro model predicts rural-urban migration continues until:
- Urban unemployment reaches zero
- Expected urban income (wage × employment probability) equals rural income
- Cities build enough housing
- Governments stop it
Migrants respond to expected income, not guaranteed wages. Urban unemployment is the equilibrating mechanism — it persists in equilibrium rather than signaling failure.
Q2. Agglomeration economies raise productivity through all of the following EXCEPT:
- Sharing infrastructure and suppliers
- Better matching of specialized workers and firms
- Knowledge spillovers from proximity
- Higher rural crop yields
Sharing, matching, and learning are Marshall's three agglomeration forces. Rural yields are unrelated — agglomeration is a purely urban phenomenon.
Q3. Evidence on slum policy most strongly supports:
- Forced clearance and relocation
- In-situ upgrading: water, sanitation, tenure security, and services
- Banning rural-urban migration
- Ignoring slums entirely
Clearance destroys livelihoods without solving affordability; upgrading improves health and welfare cost-effectively while preserving residents' location advantages and networks.
Click a question to reveal the answer and explanation.
Frequently asked questions
What is the Harris-Todaro paradox?
Creating urban jobs can raise urban unemployment: new jobs attract more migrants than jobs created, since migration responds to expected income. Job schemes must account for the migration response.
Why is housing so expensive in successful cities?
Productivity gains raise land values, but restrictive zoning (height limits, lengthy approvals) prevents supply from responding — turning agglomeration gains into landowner rents. Upzoning near transit is the standard fix.
What is land-value capture?
Funding infrastructure from the land-value gains it creates — via betterment levies, tax-increment financing, or public land leasing (Hong Kong's MTR funds railways from station-area development).
Are African cities urbanizing differently?
Yes — 'urbanization without industrialization': people move to cities for services and informal work without the manufacturing boom that absorbed Asia's migrants, creating consumption cities funded by resource rents and aid.