BharatNotes
Overview
World population crossed 8 billion in November 2022 and stands at approximately 8.2 billion as of 2025 (UN estimates). Understanding population distribution, growth patterns, demographic transition, and urbanisation is critical for GS1 (Geography) and GS1 (Society) — UPSC tests both factual knowledge (top countries, megacities) and analytical ability (causes and consequences of urbanisation, demographic dividend vs demographic burden).
World Population — Distribution and Growth
Most Populous Countries (2025)
| Rank | Country | Population (approx.) | Key Fact |
|---|---|---|---|
| 1 | India | ~1,457 million | Overtook China as world's most populous country in 2023 |
| 2 | China | ~1,418 million | Population declining since 2023 — first decline since the Great Famine (1959–61) |
| 3 | United States | ~346 million | Growth driven primarily by immigration |
| 4 | Indonesia | ~285 million | Largest population in Southeast Asia |
| 5 | Pakistan | ~274 million | One of the fastest-growing major populations |
| 6 | Nigeria | ~235 million | Projected to become 3rd most populous by 2050 |
| 7 | Brazil | ~212 million | Largest in South America; fertility declining |
| 8 | Bangladesh | ~175 million | Among the most densely populated countries |
| 9 | Russia | ~144 million | Declining population; ageing crisis |
| 10 | Ethiopia | ~134 million | Fastest-growing in the top 10 |
For Prelims: India overtook China as the most populous country in 2023. The top 10 countries together contain approximately 57% of the world's population. China's population has been declining since 2023 — its one-child policy (1979–2015) created a demographic time bomb.
Factors Affecting Population Distribution
| Factor | High Density | Low Density |
|---|---|---|
| Climate | Temperate, tropical monsoon regions | Extreme cold (Siberia, Antarctica), extreme heat (Sahara), extreme aridity |
| Relief | Plains and river valleys (Indo-Gangetic, Nile, Yangtze) | Mountains (Himalayas, Andes), plateaus (Tibetan Plateau) |
| Soil and agriculture | Fertile alluvial, volcanic soils | Infertile, rocky, or frozen soils |
| Water availability | River basins, coastal areas | Deserts, interior continental regions |
| Economic opportunity | Industrial and commercial centres, port cities | Remote, resource-poor regions |
| Historical factors | Ancient civilisation centres (Nile, Indus, Yellow River) | Historically uninhabited or sparsely settled areas |
Demographic Transition Model (DTM)
The Demographic Transition Model, developed by Warren Thompson (1929), describes how populations change as societies industrialise and modernise.
Five Stages
| Stage | Birth Rate | Death Rate | Growth | Characteristics | Examples |
|---|---|---|---|---|---|
| Stage 1 — Pre-industrial | High | High | Minimal / zero | Subsistence agriculture, no modern medicine, high infant mortality | No country today; only the most isolated tribal communities |
| Stage 2 — Early expanding | High | Falling rapidly | Rapid growth | Improved sanitation, medicine, food supply reduce deaths; births remain high | Many sub-Saharan African countries (Niger, Mali, Chad) |
| Stage 3 — Late expanding | Falling | Low | Slowing growth | Urbanisation, education (especially of women), access to contraception reduce births | India, Bangladesh, Indonesia, many developing countries |
| Stage 4 — Low stationary | Low | Low | Near zero / stable | Post-industrial society; family planning widespread; ageing population emerges | USA, UK, France, Australia, most developed countries |
| Stage 5 — Declining | Very low (below replacement) | Low (but rising due to ageing) | Negative | Fertility well below replacement level (2.1); elderly outnumber young; labour shortages | Japan, Germany, Italy, South Korea, Croatia, Portugal |
For Mains: The DTM is a useful framework but has limitations: (1) It was developed from European historical experience and may not apply universally; (2) Some countries have jumped stages rapidly (China, Thailand, Brazil); (3) Some African countries appear "stuck" in Stage 2 due to poverty, conflict, and disease; (4) Stage 5 was not in the original model — it was added later to account for below-replacement fertility in developed countries.
Key Demographic Concepts
| Concept | Definition |
|---|---|
| Crude Birth Rate (CBR) | Number of live births per 1,000 population per year |
| Crude Death Rate (CDR) | Number of deaths per 1,000 population per year |
| Total Fertility Rate (TFR) | Average number of children born to a woman over her lifetime |
| Replacement level fertility | TFR of approximately 2.1 — the level at which a population exactly replaces itself (accounting for infant mortality) |
| Dependency ratio | Ratio of dependents (aged 0–14 and 65+) to the working-age population (15–64) |
| Demographic dividend | Economic growth potential when the working-age share of the population is large relative to dependents — India is in this window (2020s–2040s) |
| Population momentum | Population continues to grow even after fertility falls to replacement level, because a large cohort of young people is still entering reproductive age |
World Urbanisation
Global Urbanisation Trends
| Metric | Figure | Source |
|---|---|---|
| Urban population share (2025) | ~45% in cities, 36% in towns (UN WUP 2025) | UN World Urbanization Prospects 2025 |
| Urban population (1950) | ~30% of world population | UN |
| Projected urban population (2050) | ~68% of world population | UN |
| Urban growth concentration | Two-thirds of world population growth between now and 2050 will occur in cities | UN WUP 2025 |
Urbanisation by Region
| Region | Urban % (approx. 2025) | Trend |
|---|---|---|
| North America | ~83% | Highly urbanised; growth now in suburbs and exurbs |
| Latin America | ~82% | Among the most urbanised developing regions; rapid 20th-century urbanisation |
| Europe | ~75% | Stable; some counter-urbanisation in Western Europe |
| East Asia | ~65% | China's urban population grew from 26% (1990) to ~65% (2025) — one of the fastest urbanisation episodes in history |
| Southeast Asia | ~52% | Rapidly urbanising; Jakarta, Bangkok, Manila as megacity drivers |
| South Asia | ~37% | Still predominantly rural; India ~36% urban; urbanisation accelerating |
| Sub-Saharan Africa | ~42% | Fastest-urbanising region; urban population doubling every 20 years |
Megacities and Urban Agglomerations
What Is a Megacity?
A megacity is defined as an urban agglomeration with a population of 10 million or more. The number of megacities has quadrupled from 8 in 1975 to 33 in 2025 (UN WUP 2025), with more than half located in Asia.
World's Largest Urban Agglomerations (2025, UN WUP 2025)
| Rank | City | Country | Population (approx.) |
|---|---|---|---|
| 1 | Jakarta | Indonesia | ~42 million |
| 2 | Dhaka | Bangladesh | ~37 million |
| 3 | Tokyo | Japan | ~33.4 million |
| 4 | Delhi | India | ~33 million |
| 5 | Shanghai | China | ~30 million |
| 6 | Cairo | Egypt | ~28 million |
| 7 | Beijing | China | ~27 million |
| 8 | Mumbai | India | ~26 million |
| 9 | Mexico City | Mexico | ~22 million |
| 10 | Sao Paulo | Brazil | ~22 million |
For Prelims: According to the UN WUP 2025, Jakarta is now the world's most populous city (~42 million), followed by Dhaka (~37 million) and Tokyo (~33.4 million). India has 2 cities in the top 10 — Delhi and Mumbai. The number of megacities is projected to reach 37 by 2050.
Megacity Growth Drivers
| Factor | Explanation |
|---|---|
| Rural-urban migration | Push factors (poverty, landlessness, lack of services) and pull factors (employment, education, healthcare) drive migration to cities |
| Natural increase | Urban populations grow through births exceeding deaths, especially in developing-world megacities |
| Administrative expansion | Cities annex surrounding areas — Jakarta's metro area extends far beyond the original city boundaries |
| Economic concentration | Cities generate disproportionate GDP — Delhi NCR alone contributes ~4% of India's GDP |
Urbanisation Challenges
Slums and Informal Settlements
| Aspect | Detail |
|---|---|
| Global scale | Approximately 1 billion people worldwide live in slums or informal settlements (UN-Habitat) |
| Definition | Settlements lacking one or more of: durable housing, sufficient living area, access to clean water, access to sanitation, security of tenure |
| Concentration | Sub-Saharan Africa (~56% of urban population in slums), South Asia (~31%), Southeast Asia |
| Health impacts | Overcrowding, poor sanitation, contaminated water lead to higher disease burden — cholera, dengue, tuberculosis |
Urban Heat Island (UHI) Effect
| Feature | Detail |
|---|---|
| What | Urban areas are significantly warmer than surrounding rural areas due to concrete, asphalt, reduced vegetation, waste heat from vehicles and industry |
| Magnitude | Cities can be 2–5 C warmer than surrounding countryside; during heatwaves, the difference can reach 8–10 C |
| Consequences | Increased energy demand (air conditioning), heat-related mortality, worsened air pollution (ground-level ozone formation) |
| Mitigation | Green roofs, urban forests, cool pavements, water bodies, improved building design |
Traffic and Air Pollution
| Challenge | Detail |
|---|---|
| Traffic congestion | Megacities in developing countries face severe congestion — Mumbai, Delhi, Jakarta, Lagos among the worst globally |
| Air pollution | Urban transport, industry, and construction generate PM2.5, NO2, and ozone — Delhi regularly records AQI above 400 (hazardous) during winter |
| Solutions | Mass transit (metro, BRT), congestion pricing, electric vehicles, non-motorised transport infrastructure, land-use planning to reduce commute distances |
Water Stress and Waste Management
| Challenge | Detail |
|---|---|
| Water stress | Many megacities face chronic water shortages — Cape Town's "Day Zero" (2018), Chennai water crisis (2019), Mexico City sinking due to groundwater extraction |
| Solid waste | Megacities generate thousands of tonnes of waste daily; inadequate waste management leads to open dumping, groundwater contamination, and methane emissions |
| Wastewater | In developing countries, 80% of wastewater is discharged untreated into water bodies (UN) |
Sustainable Urban Development
New Urban Agenda
| Feature | Detail |
|---|---|
| Adopted | Habitat III, Quito, Ecuador, October 2016 |
| Purpose | Provides a comprehensive framework for sustainable urbanisation — planning, construction, governance, and management of cities |
| Vision | Cities that are inclusive, safe, resilient, and sustainable — "cities for all" |
| Link to SDGs | Acts as an accelerator for SDG 11 and other urban-related goals |
SDG 11 — Sustainable Cities and Communities
| Target | Focus Area |
|---|---|
| 11.1 | Safe and affordable housing for all |
| 11.2 | Affordable and sustainable transport systems |
| 11.3 | Inclusive and sustainable urbanisation; participatory planning |
| 11.4 | Protect cultural and natural heritage |
| 11.5 | Reduce deaths from natural disasters in cities |
| 11.6 | Reduce environmental impact of cities (air quality, waste management) |
| 11.7 | Universal access to safe, inclusive green and public spaces |
Smart Cities — Global Examples
| City | Country | Key Feature |
|---|---|---|
| Singapore | Singapore | Integrated smart traffic, water recycling, green building standards, digital governance |
| Copenhagen | Denmark | Carbon-neutral target by 2025; cycling infrastructure; district heating from waste incineration |
| Barcelona | Spain | IoT-enabled street lighting, smart waste bins, open data platforms |
| Seoul | South Korea | Digital governance, smart transport (T-money), automated waste collection |
| Songdo | South Korea | Purpose-built smart city; pneumatic waste collection; central sensor network |
For Mains: "Smart cities" is not just about technology — it is about using technology to solve urban governance problems. India's Smart Cities Mission (2015) covers 100 cities, but progress has been uneven. The lesson from global examples is that technology must be embedded in good urban planning, not used as a substitute for it.
Counter-Urbanisation and Ageing
Counter-Urbanisation
| Feature | Detail |
|---|---|
| Definition | Movement of people from cities to rural or semi-rural areas — the reverse of urbanisation |
| Causes | Remote work (accelerated by COVID-19), high urban housing costs, desire for better quality of life, environmental concerns |
| Regions | Most visible in developed countries — USA (migration from coastal cities to mid-sized towns), UK, parts of Western Europe |
| Implications | Revitalisation of rural economies; but also gentrification of rural areas, strain on rural infrastructure, loss of farmland |
Ageing Population — Global Challenge
| Country/Region | Median Age (2025) | Key Facts |
|---|---|---|
| Japan | ~49 years | World's oldest population; ~30% aged 65+; declining workforce; "super-aged society" |
| Germany | ~46 years | Reliance on immigration to fill labour shortages; pension system under stress |
| Italy | ~47 years | Lowest fertility in Europe (~1.2 TFR); rural depopulation |
| South Korea | ~44 years | World's lowest TFR (~0.7 in 2024); projected to halve population by 2100 |
| China | ~39 years | Ageing rapidly due to one-child policy legacy; working-age population shrinking since 2015 |
Consequences of Ageing
| Impact | Detail |
|---|---|
| Labour shortage | Shrinking workforce reduces economic output; increases dependency ratio |
| Pension burden | Fewer workers supporting more retirees; pension systems face insolvency |
| Healthcare costs | Elderly require more medical care — chronic diseases, long-term care |
| Social impact | Loneliness epidemic among elderly; changing family structures |
| Policy responses | Raising retirement age, encouraging immigration, pro-natalist policies (cash incentives for children), automation to compensate for labour loss |
For Mains: Ageing is the "silent crisis" of the 21st century. While India is currently benefiting from its demographic dividend (median age ~28), it must learn from Japan, South Korea, and Europe. India's own southern states (Kerala, Tamil Nadu) are ageing faster than northern states — creating an intra-national demographic divergence that has political implications (delimitation debate).
UPSC Relevance
Prelims Focus Areas
- World population crossed 8 billion in November 2022; ~8.2 billion in 2025
- India overtook China as most populous country in 2023
- Top 3 most populous: India, China, USA
- Megacity = 10 million+ population; 33 megacities in 2025 (UN WUP 2025)
- Jakarta is the world's most populous city (~42 million, 2025)
- DTM: 5 stages; Stage 5 = below-replacement fertility (Japan, Germany)
- New Urban Agenda: adopted at Habitat III, Quito, 2016
- SDG 11: Sustainable Cities and Communities
- South Korea's TFR ~0.7 (2024) — world's lowest
Mains Focus Areas
- Urbanisation as both opportunity and challenge — economic growth vs slums, pollution, inequality
- Demographic dividend vs demographic burden — India's window of opportunity and the risk of missing it
- Megacity governance challenges — water, waste, transport, housing, pollution
- Smart cities — technology as enabler vs technology as substitute for governance
- Ageing populations in developed countries — lessons for India's future
- Counter-urbanisation post-COVID — implications for urban and rural planning
- Intra-national demographic divergence (India's north-south fertility gap)
Vocabulary
Megacity
- Pronunciation: /ˈmɛɡəsɪti/
- Definition: An urban agglomeration with a total population of 10 million or more inhabitants, characterised by enormous economic output, complex governance challenges, and significant socio-environmental pressures including congestion, pollution, and housing stress.
- Origin: The prefix mega- from Greek megas (μέγας, "great, large") combined with city from Old French cite, from Latin civitas ("community of citizens"); the term gained currency in the 1970s–80s as cities like Tokyo, New York, and Mexico City crossed the 10-million threshold.
Demographic Dividend
- Pronunciation: /ˌdɛməˈɡræfɪk ˈdɪvɪdɛnd/
- Definition: The economic growth potential that arises when a country's working-age population (15–64 years) is significantly larger than its dependent population (children and elderly), resulting in higher per-capita productivity, savings, and investment — provided the workforce is educated, skilled, and employed.
- Origin: The concept was developed by demographers David Bloom and David Canning in the late 1990s; the term "dividend" reflects the economic bonus a nation receives from favourable age structure — India's demographic dividend window is estimated at roughly 2020s–2040s.
Urbanisation
- Pronunciation: /ˌɜːrbənaɪˈzeɪʃən/
- Definition: The process by which an increasing proportion of a country's population comes to live in urban areas, driven by rural-to-urban migration, natural increase within cities, and the reclassification of rural areas as urban — accompanied by economic, social, and environmental transformation.
- Origin: From Latin urbanus ("of the city"), from urbs ("city"); the term entered English in the mid-19th century during the rapid urbanisation of the Industrial Revolution — globally, the urban share of population has risen from ~30% in 1950 to ~45% in cities by 2025.
Key Terms
Urban Heat Island (UHI)
- Pronunciation: /ˈɜːrbən hiːt ˈaɪlənd/
- Definition: A phenomenon in which urban areas experience significantly higher temperatures (2–5 C or more) than surrounding rural areas, caused by the absorption and re-radiation of heat by concrete, asphalt, and buildings, combined with reduced vegetation cover and waste heat from vehicles, industry, and air conditioning.
- Context: UHI intensifies during heatwaves and is a growing public health concern in megacities; mitigation strategies include green roofs, urban forests, cool pavements, and water bodies — studies show that urban greening can reduce UHI by 1–3 C.
- UPSC Relevance: GS1 (Geography, Urbanisation). Prelims: definition and causes. Mains: asked in the context of urban climate challenges, heatwave management, and sustainable city planning — often linked to SDG 11 and India's Smart Cities Mission.
New Urban Agenda
- Pronunciation: /njuː ˈɜːrbən əˈdʒɛndə/
- Definition: A comprehensive global framework for sustainable urbanisation adopted at the United Nations Conference on Housing and Sustainable Urban Development (Habitat III) in Quito, Ecuador, in October 2016, providing standards and principles for the planning, construction, development, management, and improvement of urban areas worldwide.
- Context: The New Urban Agenda acts as an accelerator for SDG 11 (Sustainable Cities and Communities) and links to multiple other SDGs; it emphasises inclusive, safe, resilient, and sustainable cities through participatory planning, equitable land use, and integrated urban governance.
- UPSC Relevance: GS1 (Geography, Urbanisation), GS2 (Governance). Prelims: adopted at Habitat III, Quito, 2016. Mains: asked to discuss frameworks for sustainable urbanisation — the New Urban Agenda provides the global policy context, while India's Smart Cities Mission, AMRUT, and PMAY are domestic implementations.
Sources: United Nations World Urbanization Prospects 2025 (WUP 2025), UN Population Division — World Population Prospects 2024 Revision, UN-Habitat, worldometers.info, Our World in Data — Demographic Transition, Statista, NCERT — Fundamentals of Human Geography
