Measuring population change

Natural increase is the difference between the crude birth rate and crude death rate; migration is excluded. These rates are usually measured per 1,000 people per year. If deaths outnumber births, natural decrease occurs.

To calculate overall population change, migration must also be included:

Population change = births − deaths + immigration − emigration

A country may therefore have natural decrease and still grow because of positive net immigration. The reverse can also happen: net emigration may reduce rapid natural increase.

Total fertility rate is the average number of children a woman is expected to have during her reproductive life, assuming current age-specific fertility rates continue. In many populations, replacement-level fertility is approximately 2.1 children per woman, though this varies with mortality.

Life expectancy is the average number of years a newborn is expected to live if current mortality patterns continue. Nutrition, sanitation and health care all affect it, as do income, education, conflict and disease.

Demographic transition over time

Demographic transition is the shift from high birth and death rates to low birth and death rates as a population experiences social and economic change. The demographic transition model presents a typical sequence, not a timetable that every country must follow.

• In the first stage, both birth and death rates are high. Natural increase is therefore low.
• Death rates fall first as food supply, sanitation and health care improve. Birth rates remain high, causing rapid natural increase.
• Birth rates decline later due to urbanization, female education and access to contraception. Lower infant mortality and the rising cost of raising children also contribute.
• Eventually, birth and death rates are both low, so growth becomes slow or stable.
• In some countries, fertility stays below replacement level. Deaths may then exceed births, leading to natural decrease and population ageing.

Population structure and dependency

Population structure describes the composition of a population, especially by age and sex. A population pyramid commonly represents this structure, showing males and females separately in five-year age groups.

A broad-based pyramid points to high fertility and a large youthful population. If the base is narrow and the middle wider, fertility is declining. A relatively wide upper section shows high life expectancy and an ageing population. Irregular shapes may reflect migration, war, disease or a past baby boom.

Dependency ratio compares the number of people conventionally classed as dependants with the working-age population:

Dependency ratio = ((population aged 0–14 + population aged 65 and over) ÷ population aged 15–64) × 100

A high youth dependency ratio puts strong pressure on schools and child health care, while also creating demand for future employment. A high old-age dependency ratio raises demand for pensions, health care and social care. However, the measure is only an approximation. Some working-age people aren’t employed, while some younger and older people do work.

Contrasting country examples

Detailed examples should link demographic indicators to population structure and show how they change over time. The pair below is illustrative; retain the contrasting countries studied in class.

Around the late 2010s, Nigeria’s total fertility rate was above five children per woman, while life expectancy was in the mid-50s. Japan had fertility of roughly 1.4 and life expectancy above 80 years. These figures help explain the strong contrast between their population pyramids and dependency burdens.

The influence of each process shifts over time. Falling mortality initially speeds up population growth; later, fertility decline slows it. Migration may then become a major influence on the size and structure of particular age groups.

Rapid urban growth

A megacity is an urban agglomeration of at least 10 million inhabitants. Population growth may come from natural increase or rural–urban migration, as well as migration from smaller towns. The outward physical expansion of the built-up area also contributes.

This growth can outpace the expansion of housing, transport, water supply, sanitation and public services. The effects aren’t shared evenly. A city may create employment and encourage innovation while poorer residents face overcrowding and environmental hazards.

Consequences for individuals

Rapid urban growth may improve access to paid work, education, health care, markets and social networks. Large urban economies provide formal jobs alongside informal opportunities, including street trading, transport services and small-scale manufacturing.

Migrants without secure incomes, however, may end up in low-paid informal work with little legal protection. When affordable housing is scarce, overcrowding, insecure tenure and informal settlements can result. Congestion, unreliable transport and long journeys leave less time for work, education and family life.

If water and sanitation systems fail to keep pace, people face greater exposure to contaminated water, disease and flooding. Income, age, gender and location shape these effects. Wealthier residents can often pay for safer housing and private services.

Consequences for society

At the city scale, a large, concentrated population can sustain specialized services, major transport systems and a diverse labour market. Businesses have access to more workers and consumers. Cultural exchange may also encourage creativity and entrepreneurship.

Yet this concentration puts roads, schools, hospitals, drainage, waste collection and energy supply under heavy pressure. Informal construction may extend onto floodplains, wetlands or unstable slopes. Industry and traffic add to air pollution, while poor waste disposal contaminates land and water.

As the city spreads, it can absorb farmland and natural habitats. Rapid expansion may deepen social and spatial inequality, leaving well-serviced districts close to settlements with poor services. Whether growth is mainly an opportunity or a burden depends on job creation, infrastructure provision and how access to services is distributed.

Illustrative case study: Lagos

Lagos is a contemporary megacity in Nigeria. Its population has grown rapidly through natural increase and migration from other parts of Nigeria and neighbouring countries. As a commercial, financial and port centre, it attracts people looking for employment and education.

Benefits include a large labour force, extensive markets and expanding service industries. There are opportunities in formal and informal economic activity, while the city links Nigeria to international flows of trade, investment and people.

Affordable housing and infrastructure haven’t kept pace with growth. Many residents face congestion, long commutes, unreliable basic services and insecure informal employment. Low-income settlements, including waterside communities, may be especially vulnerable to flooding, poor sanitation and the threat of eviction. The costs are not shared equally across Lagos.

A case study should present both sides of change, covering consequences for individual residents and for wider urban society. It should identify who benefits, who bears the costs and how outcomes vary between neighbourhoods.

Forms of forced movement

Forced migration happens when people are compelled to leave their homes because staying would threaten their lives, safety or livelihoods. Unlike voluntary migration, it leaves people with very little meaningful choice.

Internal displacement describes forced movement within a person’s own country. Although internally displaced people haven’t crossed an international frontier, their needs may be much the same as those of people displaced abroad.

Forced movement can be temporary, repeated or long term. While some people travel directly to safety, others make several internal and international moves as conditions change.

Push factors

Political push factors include armed conflict, persecution, state repression, political violence and serious insecurity. Some people flee because they have been directly targeted. Others leave after public order, employment and essential services collapse.

Environmental push factors range from sudden hazards such as storms, floods, earthquakes and wildfires to slower changes such as drought, land degradation and loss of water supplies. Human and environmental causes often overlap. Drought, for example, is more likely to displace people where poverty, weak governance or conflict already restricts their ability to adapt.

Consequences for people and places

The immediate effects on displaced people may include injury, family separation, loss of housing, interrupted education, unemployment and psychological trauma. While travelling, migrants may also encounter exploitation, trafficking, violence or dangerous routes.

Places of origin can lose workers, skills and consumers. Settlements may be abandoned, social networks broken, and farming or other production may decline. In some cases, reduced pressure on local resources or remittances from displaced family members partly offsets these losses.

Receiving places benefit from labour, entrepreneurship and cultural diversity. Yet rapid arrivals can put pressure on housing, schools, health care, employment and water supplies, particularly when the receiving population is already vulnerable. Scarce resources, or a perception that access is unequal, can create tension.

With internal displacement, primary responsibility remains with the affected country. Its government, however, may have limited capacity or may be involved in the political causes. International movement shifts some consequences across borders and creates spatial interaction between origins, transit locations and destinations.

Illustrative political example: displacement from Syria

The conflict that began in 2011 forced millions of Syrians from their homes. By the late 2010s, more than six million people were internally displaced, while millions more had crossed borders, particularly into nearby countries.

Push factors included armed conflict, insecurity, persecution and the destruction of homes and services. Displaced people faced family separation, disrupted schooling, lost livelihoods and dependence on temporary accommodation or assistance. Areas of origin lost population and economic activity. Meanwhile, receiving towns and cities experienced greater demand for housing, education, health care and employment, although new workers and businesses also contributed to some local economies.

Illustrative environmental example: Typhoon Haiyan in the Philippines

Typhoon Haiyan caused extensive storm-surge and wind damage in 2013, displacing about four million people within the Philippines. It destroyed homes, fishing equipment, businesses and public infrastructure, especially in exposed coastal settlements.

Most movement took place internally through evacuation, temporary shelter and relocation to other settlements. People lost income, education was interrupted, and host communities came under pressure. Some residents returned to rebuild. Others stayed away because employment, housing or perceptions of safety had changed.

The two examples show a clear contrast: a prolonged, politically driven movement involving both internal and cross-border displacement, and a sudden environmental disaster that produced mainly internal movement. Your class examples should include evidence of the push factors, routes and consequences for origin and receiving places.

Categorizing impacts

Population change produces many impacts, so organize them into categories rather than presenting one long, undifferentiated list. Useful categories include:

• Demographic: population size, age structure, sex structure and dependency.
• Social: housing, health, education, family networks and community relations.
• Economic: employment, labour supply, wages, public spending and markets.
• Environmental: land conversion, waste, pollution and pressure on water or ecosystems.
• Political: access to rights and services, representation and pressure on decision-makers.

One impact may belong to several categories. An ageing population, for instance, is demographic. Its effects on pension spending and health care are economic and social.

Impacts may also be positive or negative, direct or indirect, and short term or long term. How they are classified depends partly on perspective. Rapid population growth may provide employers with a larger labour supply, yet intensify competition for work among individuals. Migration can reduce population pressure at an origin while causing labour shortages there.

Scale and spatial interaction

Spatial interaction is the movement and connection between places through flows such as people, money, goods and information. As a result, population change in one place can have consequences elsewhere.

At the local scale, migration may alter demand for housing or schools in a neighbourhood. Internal migration can redistribute working-age adults between regions at the national scale. At the international scale, forced migration may connect origin, transit and destination countries. Always link impacts to the scale and group under consideration.

Choosing an appropriate graphical representation

Each type of graph reveals a different aspect of population change:

Graphs need a suitable scale, labelled axes, units, a title and a clear key. Don’t confuse absolute totals with relative measures. A country may receive many migrants in total but still have a small migrant share because its population is much larger.

A line graph can compare demographic change across contrasting countries. Focus on the overall trend, turning points, rate of change and differences between lines rather than isolated values. When birth and death rates are plotted together, they reveal changes in the size of natural increase.

Population pyramids allow impacts to be inferred from population structure. A wide base suggests demand for maternal services and schools. A large working-age group indicates potential labour supply, while a wide upper section suggests rising demand for pensions and elderly care. These are reasoned interpretations, not automatic outcomes.

Flow maps show spatial interaction by connecting origins and destinations. Arrow direction indicates movement; arrow width can represent volume. If national borders are visible, these maps can distinguish internal movement from international movement.

Interpreting impacts carefully

A strong interpretation first identifies the pattern, then supports it with evidence from the graph and explains the relevant process. Correlation alone doesn’t prove causation. Fertility and economic development, for example, may change together, but education, urbanization, health care and gender relations help explain their relationship.

Categories shown on graphs can hide inequalities. A city-wide average may conceal large differences between neighbourhoods. Likewise, a national dependency ratio may mask regional variations and the fact that not every working-age person is employed. Match the representation to the scale and purpose of the analysis.