Band 8 model answer

The emergence of mega-cities, urban areas with populations exceeding ten million, has placed extraordinary demands on infrastructure that was never designed to accommodate such scale. The causes of this growth and the measures required to manage it deserve careful consideration.

Rapid urbanisation is driven primarily by the concentration of economic opportunity in large cities. Employers, universities, hospitals and government services cluster in capital cities and regional hubs, creating powerful incentives for internal migration from rural areas and smaller towns. In many developing countries, inadequate investment in regional development means that a single mega-city often accounts for the overwhelming share of a nation's GDP and employment, drawing in migrants faster than the city can absorb them. Natural population growth within cities, where birth rates remain relatively high in low-income urban neighbourhoods, further accelerates the pace of expansion.

The infrastructure consequences are severe and self-reinforcing. Transport networks become gridlocked as private car ownership rises faster than road capacity, worsening air pollution and reducing the productivity of commuters who spend hours travelling short distances. Water and sanitation systems are overwhelmed, particularly in informal settlements that grow on city peripheries without planned connections to public utilities. These failures in turn repel investment and skilled workers, reinforcing the cycle of decline in districts that need investment most.

Effective responses require both metropolitan and national strategies. Within cities, investment in mass rapid transit, as demonstrated by the success of metro systems in cities such as Bogotá and Addis Ababa, can dramatically reduce congestion while improving accessibility. Urban planning frameworks must incorporate informal settlements rather than ignoring them, providing basic services and tenure security. At the national level, deliberate decentralisation, moving government agencies, universities and businesses to secondary cities, can redistribute growth and relieve pressure on mega-cities before infrastructure crises become irreversible.