Mexico City megacity GCSE geography — urban growth, inequality and sustainability

Mexico City is one of the Western Hemisphere's largest cities, with a population of over 21 million in the metropolitan area. Built on a drained lakebed at 2,240 metres altitude, it combines rapid economic growth with persistent problems of air pollution, water scarcity, and earthquake risk — a classic megacity challenge.

What is a megacity and why does Mexico City qualify?

A megacity is a city with a population of 10 million or more. Mexico City's metropolitan area — the city proper plus surrounding urban municipalities — houses approximately 21 million people, making it the largest city in North America and one of the 10 largest metropolitan areas in the world. It is the political, economic and cultural capital of Mexico, generating around 17–18% of Mexico's entire GDP.

Mexico City exemplifies many of the characteristics geographers associate with megacities in lower-middle-income countries: rapid growth driven by rural-to-urban migration; extreme wealth alongside extreme poverty; stretched infrastructure; and environmental pressures intensified by scale.

How did Mexico City grow so rapidly?

Mexico City grew rapidly through most of the 20th century because of industrialisation and the gap between rural and urban incomes. Push factors drove rural Mexicans out of agriculture — land poverty, drought, lack of services — while pull factors drew them to the city: factory jobs, better healthcare, schools and greater economic opportunity. This rural-to-urban migration is a pattern repeated in megacities across Latin America, Africa and Asia.

Growth has slowed since the 1990s as fertility rates declined and migration patterns changed, but the city's existing population continues to require expanding housing, services and infrastructure.

What are the problems created by Mexico City's physical geography?

Mexico City's location creates unusual physical hazards.

The lakebed foundation: the city was built on the drained bed of Lake Texcoco, the lake on which the Aztec capital Tenochtitlan stood. Lakebed sediments are soft and compressible. As the city extracts groundwater to supply its population, the ground compresses — a process called subsidence. Parts of the city centre have sunk by 9 metres or more since the early 20th century. Buildings tilt, infrastructure cracks, and flood risk increases as the ground sinks below river and drainage canal levels.

Earthquake risk: Mexico City sits in a seismically active region, and the soft lakebed sediments amplify earthquake waves. The catastrophic 1985 earthquake (magnitude 8.1) killed an estimated 5,000–10,000 people and destroyed thousands of buildings. Another serious earthquake struck in September 2017 (magnitude 7.1), killing over 300 people. The soft geology means that even moderate earthquakes at a distance can cause severe shaking in Mexico City while causing little damage elsewhere.

Air basin: the city sits in a high-altitude mountain basin, surrounded by volcanoes. The basin geography, combined with high altitude (meaning thinner air), trapped car exhaust and industrial pollution for decades. In the early 1990s, Mexico City's air quality was among the worst in the world, with children warned not to play outside on many days.

What are the social and economic challenges of Mexico City?

Using the SEEP framework:

How has Mexico City tried to manage its problems?

Air quality improvements: Mexico City's air quality has improved dramatically since the early 1990s through: replacing petrol with unleaded fuel; introducing vehicle emissions testing; expanding the metro and bus rapid transit systems; creating cycling infrastructure; relocating or closing heavily polluting factories.

Water management: the city has expanded water recycling and water recapture programmes. Aquifer injection — pumping treated water back underground — attempts to slow subsidence. Water restrictions and tariff reforms encourage conservation. The ancient Aztec system of canals in Xochimilco (a UNESCO World Heritage Site) has been partly restored to manage local water and maintain traditional "floating garden" agriculture.

Earthquake preparedness: building codes were significantly strengthened after 1985. The city runs one of the world's most extensive earthquake early warning systems (SASMEX), which can give central Mexico City up to 120 seconds of warning before shaking arrives from offshore Pacific earthquakes.

Transport investment: the metro system carries around 5 million passengers per day; a Bus Rapid Transit (Metrobús) network adds capacity; cycle hire schemes have expanded in central areas.

Frequently asked questions

What is a favela — and does Mexico City have the equivalent?

A favela is the Portuguese/Brazilian term for an informal settlement. Mexico City uses terms such as colonia popular or vecindad (tenement block). These are areas where migrants settled without formal land ownership, built housing incrementally from available materials, and lacked piped water, sewerage, electricity and paved roads for years or decades. Many have since been consolidated — residents have gained land titles, utilities have been extended — in a process called urban consolidation. Around a third of Mexico City's population lives in consolidated former informal settlements.

Why is Mexico City's water supply such a serious problem?

Mexico City imports roughly 40% of its water from outside the basin, through a major aqueduct system. The remaining 60% is extracted from an aquifer that is being depleted much faster than it is replenished. This over-extraction causes both the subsidence described above and the long-term risk of running out of accessible groundwater. The city also leaks an estimated 40% of its piped water supply through ageing, damaged pipes — another consequence of decades of subsidence damaging infrastructure. Water poverty — inadequate access to safe running water — affects millions of residents in peripheral areas who rely on private water tanker deliveries at much higher prices than piped water.

How does Mexico City compare with other megacities such as Lagos or Mumbai?

Mexico City, Lagos and Mumbai all share characteristics of rapid growth, informality and inequality, but differ significantly. Mexico City is the wealthiest of the three by GDP per capita; it has a more extensive formal infrastructure (particularly its metro); and its growth has slowed. Lagos (Nigeria) is growing faster and has less formal infrastructure. Mumbai (India) combines extreme poverty in some of the world's largest informal settlements with one of Asia's most dynamic financial and industrial economies. Each megacity reflects its country's specific combination of income level, colonial history, governance quality and geographic constraints.

Has Mexico City's population stopped growing?

Growth has slowed considerably from its mid-20th century peak rate, when the population could double within 15–20 years. The rate slowed as Mexico's fertility rate declined from over 6 children per woman in 1970 to under 2.2 by the 2010s, and as economic opportunities in other Mexican cities grew. However, absolute growth continues — adding hundreds of thousands of people per decade. The inner city has actually been losing population to outer suburban and peri-urban areas, as wealthier residents moved out and poorer migrants settled in expanding outer zones, creating a "doughnut" pattern of depopulation at the centre and growth at the edges.

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