G.4 Building sustainable urban systems for the future

The city has lost 25% of its total population — this qualifies as urban shrinkage, an absolute and sustained population decline, not merely slower growth.

Urban shrinkage in MEDCs results from two interacting processes: natural decrease (deaths exceeding births due to low fertility) and net out-migration, specifically the departure of younger, economically active residents seeking employment elsewhere.

Rust Belt cities lost their industrial economic base (steel, manufacturing) through deindustrialisation. Job losses prompted working-age adults to leave, skewing the age structure older and depressing birth rates further — a self-reinforcing spiral.

The option describing low fertility rates and selective out-migration of younger working-age adults captures both processes and matches the demographic mechanism of Rust Belt shrinkage.

The question asks for the combination of demographic processes that explains an absolute, sustained urban population decline in a former MEDC industrial city.

Shrinking MEDC cities are characterised by low, not high, birth rates. Elderly residents are also the group least likely to migrate away. This option contradicts the known demographic pattern.

In-migration of retirees would add population rather than reduce it, and falling death rates alone would support population stability or growth, not decline. This option is logically inconsistent with shrinkage.

Rural-to-urban migration is the dominant driver of urban growth in LEDCs, not MEDC shrinking cities. A Rust Belt city would not receive large rural migrant flows sufficient to complicate its decline.

'Low fertility rates and selective out-migration of younger working-age adults' is the only option that accurately combines the natural decrease and migration-driven decrease responsible for MEDC urban shrinkage.

The question focuses on absolute urban population growth to 2050, not which regions are already the most urbanised.

Asia and Africa have the largest and fastest-growing total populations, combined with relatively low current levels of urbanisation. This creates the greatest scope for rapid urban growth as rural residents migrate to cities in search of employment and services.

Europe and North America already have very high urbanisation rates (most people already live in cities), so their absolute urban growth potential is limited. The fastest rates of increase are in regions with large rural populations still transitioning to urban life.

Asia and Africa, with rural–urban migration as the primary driver, are consistently identified in global projections as the centres of fastest urban population growth to 2050.

The question asks which two regions will see the fastest absolute urban population growth to 2050, and what drives it.

These highly developed regions already have urbanisation rates above 75–80%. Their cities are experiencing slow growth, population aging, or in some cases shrinkage — not the fastest projected urban growth.

South America is already highly urbanised, so while cities there grow, the rate of change is slower than in Africa and Asia. Australia has a small total population, making its absolute urban growth modest in global terms.

Many Eastern European cities are experiencing population stagnation or decline associated with out-migration and aging, not rapid urban growth driven by rural–urban migration.

'Asia and Africa, driven primarily by rural–urban migration' is the only option consistent with global urbanisation projections, which identify these two regions as the fastest-growing in both absolute numbers and urban share.