Unit 2

Population and Migration Patterns and Processes: the one-page sheet

2.1 Population Distribution

Population distribution is the pattern of where people live. Most of the world’s people live in a few clusters, in East Asia, South Asia and Europe, on low, well-watered land near coasts and rivers. Physical factors and human factors shape the pattern together, and the pattern looks different at the global, national and local scales.

Where people live is called population distribution. People are not spread evenly: most live in a few large clusters, in East Asia, South Asia and Europe.
The ecumene is the part of Earth where people live permanently. Very dry, very cold and very high places lie mostly outside it.
Physical factors (climate, water, landforms, soil) and human factors (jobs, transport, government decisions, history) work together.
The pattern depends on the scale of analysis: Egypt looks crowded on a world map, but at the local scale almost everyone lives within a few kilometers of the Nile.

farmers can grow enough food there many people can live close together, and villages and towns grow trade and jobs gather there, which draws even more people the world’s people end up clustered in a few regions, with large empty areas between

population: All the people who live in a place, such as a city, a country or the whole world.
population distribution: The pattern of where people live across an area: where they are clustered and where there are few.
ecumene: The parts of Earth’s surface where people live permanently. Very cold, dry or high places lie mostly outside it.

2.2 Consequences of Population Distribution

Geographers measure crowding in three ways. Arithmetic density divides all people by all land; physiological density divides all people by arable land; agricultural density divides farmers by arable land. Carrying capacity, the number of people an area can support, is a different idea. Distribution and density affect services, society and the environment.

Arithmetic density = all people ÷ all land. Physiological density = all people ÷ arable land (land that can grow crops). Agricultural density = farmers ÷ arable land.
High physiological density means each person depends on little farmland. Low agricultural density usually means machines and large farms.
Carrying capacity is how many people an area can support without damage. It depends on technology and trade, so it is not the same as density.
Density shapes services: low density makes services far away and costly per person; high density crowds roads, housing and hospitals.

physiological density is high each person depends on very little farmland, so land is farmed hard or food is bought from other places agricultural density is low services such as clinics and schools are far apart and cost more per person

population density: The number of people for each unit of land, usually per square kilometer.
arithmetic density: The total population divided by the total land area. It shows how crowded a place is on average.
physiological density: The total population divided by the area of arable land. It shows how many people each unit of farmland must feed.
agricultural density: The number of farmers divided by the area of arable land. A low value usually means large farms that use machines.
arable land: Land that can be used to grow crops. It leaves out deserts, ice, steep mountains and built-up areas.
carrying capacity: The number of people an area can support without damaging it. It depends on resources, technology and trade, so it is not the same as density.

2.3 Population Composition

A population pyramid shows a population’s age structure and sex ratio, one cohort per bar. An expansive pyramid has a wide base and a young, growing population; a constrictive one has a narrow base and falling births. Reading the shape tells planners what a place will need next, from schools to health care, and local pyramids can look very different from national ones.

A population pyramid shows a population by age and sex: males on the left, females on the right, youngest at the bottom. Each bar is a cohort, a group born in the same years.
Age structure is how a population is split among age groups. Sex ratio is the number of males for every 100 females.
Shapes: expansive (wide base, a young, growing population), stationary (straight sides) and constrictive (a base narrower than the middle, falling births).
Bulges and dents tell stories: a baby boom, a war, or workers moving in. The pattern can differ at the local scale (a college town) from the national one.

each new cohort is bigger than the last, so the pyramid has a wide base the youngest cohorts shrink, so the base narrows the middle and top of the pyramid widen a country’s needs change: from schools and jobs to health care and pensions

population pyramid: A bar graph that shows a population by age and sex: males on the left, females on the right, youngest at the bottom.
age structure: How a population is divided among age groups, such as children under 15, people aged 15 to 64 and people 65 and over.
sex ratio: The number of males for every 100 females in a population or an age group.
cohort: A group of people born in the same years, such as everyone aged 20 to 24. Each bar of a population pyramid is a cohort.

2.4 Population Dynamics

A population changes through births, deaths and migration. The crude birth and death rates give the rate of natural increase in percent, and the rule of 70 gives doubling time. The total fertility rate compared with replacement level (about 2.1) shows long-run growth or decline. Infant mortality and life expectancy measure health, and social, cultural, political and economic forces shape every rate.

Crude birth rate (CBR) and crude death rate (CDR) are births and deaths per 1,000 people a year.
Rate of natural increase (RNI) = (CBR − CDR) ÷ 10, in percent. Migration is not part of it. Doubling time ≈ 70 ÷ RNI.
Total fertility rate (TFR) is the average number of children per woman. Replacement-level fertility is about 2.1.
Infant mortality rate (deaths under age 1 per 1,000 births) and life expectancy measure health. Social, cultural, political and economic forces shape all these rates.

the rate of natural increase is positive and the population grows infant mortality falls and life expectancy rises families have fewer children, so the total fertility rate falls each generation is smaller, and the population will shrink unless people move in

crude birth rate: The number of births in a year for every 1,000 people in a population.
crude death rate: The number of deaths in a year for every 1,000 people in a population.
total fertility rate: The average number of children a woman would have in her lifetime if the birth rates of one year stayed the same.
infant mortality rate: The number of babies who die before their first birthday for every 1,000 live births.
life expectancy: The average number of years a newborn can expect to live if the death rates of its birth year stay the same.
rate of natural increase: The crude birth rate minus the crude death rate, given as a percent (divide by 10). It leaves out migration.
doubling time: The number of years a population takes to double at a steady growth rate. By the rule of 70, it is about 70 divided by the growth rate in percent.
replacement-level fertility: The total fertility rate at which each generation just replaces itself: about 2.1 births per woman where few children die.

2.5 The Demographic Transition Model

The demographic transition model describes death rates falling first and birth rates later, in five stages, so population growth speeds up and then slows or turns negative. The epidemiological transition describes the main causes of death shifting from infections to chronic disease. Both are models built from history, with limits: place a country’s data in a stage, and say how well the model fits.

The demographic transition model (DTM) traces birth and death rates in five stages: 1 both high; 2 deaths fall; 3 births fall; 4 both low; 5 births below deaths.
A country is never "in" a stage as a fact. Its data are consistent with a stage. Low growth can mean stage 1 (high rates) or stages 4 and 5 (low rates).
The epidemiological transition traces the main causes of death: from infections and famine to chronic diseases such as heart disease and cancer, with new infections possible.
Limits: built on European history; leaves out migration; timing differs; stage 5 is not universal; it describes, it does not predict.

the death rate falls while births stay high (stage 2) the population grows very fast families have fewer children and the birth rate falls (stage 3) growth slows or stops (stage 4), and births may fall below deaths (stage 5)

demographic transition model: A model of how birth and death rates change over time in five stages: deaths fall first, then births, so population growth speeds up and then slows or turns negative.
epidemiological transition model: A model of how the main causes of death change as a society changes: from infections and famine to chronic diseases such as heart disease and cancer, with new infections possible.

2.6 Malthusian Theory

Thomas Malthus argued in 1798 that population grows faster than food, so checks such as famine, disease and war would follow. Neo-Malthusians extend the worry to other resources. Three critiques stand out: technology raised food output, fertility fell as countries changed, and hunger depends on access to food more than total supply.

Malthusian theory (Thomas Malthus, 1798): population grows faster than food, so famine, disease or war (checks) follow unless people have fewer children.
Neo-Malthusians, such as Paul Ehrlich (1968), apply the worry to water, energy and the environment.
Critiques: technology raised food output; fertility fell as countries changed; hunger comes mostly from poverty, conflict and how food is shared; trade moves food between places.
The idea links to carrying capacity: technology and trade can raise how many people an area can support.

population outruns the food supply famine, disease and war (checks) raise deaths food grows faster than Malthus expected, which weakens his theory population growth slows, another critique of Malthus

Malthusian theory: Thomas Malthus’s idea (1798) that population grows faster than the food supply, so famine, disease or war will follow unless people have fewer children.
neo-Malthusian: A later thinker who shares Malthus’s worry and extends it to water, energy and the environment, arguing that population growth should slow.

2.7 Population Policies

Governments use pronatalist policies to raise births, antinatalist policies to lower them and immigration policies to decide who may move in. Policies can be voluntary or coercive and have intended and unintended effects. Many countries, including China (1980, 2016, 2021), Singapore and Iran, switched from lowering births to raising them as fertility fell.

A pronatalist policy tries to raise births (payments, paid leave, child care). An antinatalist policy tries to lower them (family planning, limits).
An immigration policy sets who may move into a country and how many, such as Canada’s points system (1967).
Policies can be voluntary or coercive, and they have intended and unintended effects: China’s one-child policy (1980 to 2015) lowered births but also raised the sex ratio at birth.
Always date a policy. China, Singapore and Iran each moved from antinatalist to pronatalist policies as fertility fell.

a government may adopt an antinatalist policy fertility falls, sometimes below replacement level the workforce shrinks and older people become a larger share, so the government may switch to a pronatalist policy many governments also use immigration policy to fill jobs now

pronatalist policy: A government policy that tries to raise the number of births, for example with payments for each child, paid parental leave or cheaper child care.
antinatalist policy: A government policy that tries to lower the number of births, for example with family planning programs or limits on family size.
immigration policy: A government’s rules about who may move into the country, how many people and for how long.

2.8 Women and Demographic Change

More schooling, paid work, health care and contraception for women lower fertility and child deaths in most places, as in Bangladesh and Kerala, India. Changing roles also change who migrates. Ravenstein’s laws, drawn from 1800s British data, say most moves are short and step by step, every flow has a counterflow, and women moved more than men within their own country.

Female education (schooling for girls and women), paid jobs, health care and access to contraception lower fertility in most places.
Women’s changing roles also lower mortality: children of mothers with more schooling are less likely to die young.
Ravenstein’s laws of migration (1885, 1889): most moves are short, many in steps; long-distance migrants go to big cities; each flow has a counterflow; within a country women moved more than men.
Ravenstein’s limits: 1800s British data, before air travel; many more women and long-distance migrants move abroad now.

they marry and have their first child later families choose to have fewer children, so the TFR falls fewer babies and young children die more women move for work, within their country and abroad

female education: The schooling that girls and women receive. More of it is linked to later marriage, fewer children and fewer child deaths.
Ravenstein's laws of migration: Patterns of migration that E. G. Ravenstein drew from British census data in 1885 and 1889: most moves are short, many happen in steps, long-distance migrants go to large cities, each flow has a counterflow, and within a country women moved more than men.

2.9 Aging Populations

An aging population comes from fewer births and longer lives. The dependency ratio compares people under 15 and 65 and over with people of working age. Aging has economic, political and social effects, from worker shortages and pension debates to more care work in families, and it can be stronger in rural places that young people leave.

An aging population has a rising share of older people. It comes from low birth rates and longer life expectancy, and young people moving away can make one place older still.
The dependency ratio = (people under 15 + people 65 and over) ÷ people 15 to 64 × 100. Split it into youth and elderly ratios to see who the dependents are.
Effects are economic (worker shortages, pension and health costs), political (pension debates, older voters) and social (family care, empty schools).
Scale matters: rural provinces often age faster than the capital because young adults move to cities.

older people become a larger share of the population some jobs go unfilled, so firms use machines or hire workers from abroad the elderly dependency ratio rises and pensions cost each worker more governments raise the retirement age, raise taxes or cut benefits, and voters argue

aging population: A population in which older people make up a rising share, caused by low birth rates and longer lives.
dependency ratio: The number of people under 15 and 65 and over for every 100 people aged 15 to 64. The youth and elderly ratios count each group alone.

2.10 Causes of Migration

People migrate because of push factors at the place they leave and pull factors at the place they go, while intervening obstacles and opportunities along the way can block or redirect them. Causes can be cultural, demographic, economic, environmental or political, and most moves have more than one.

Migration is a long-term move to a new place to live. Push factors drive people from the origin; pull factors draw them to the destination.
Intervening obstacles (cost, distance, borders, seas, rainforest) make a move harder; intervening opportunities (a job on the way) may stop it short.
Causes are cultural, demographic, economic, environmental and political, and most moves have more than one.
Name the kind of cause and the place: "Drought in the Sahel (environmental push)" earns credit; "bad conditions" does not.

push factors make people want to leave pull factors draw people to a destination intervening obstacles slow or stop the move an intervening opportunity may make a migrant stop short

migration: A long-term move from one place to another to live, within a country or across a border.
push factor: A problem at the place a migrant leaves that drives people away, such as low pay, drought or war.
pull factor: An attraction at the place a migrant goes that draws people in, such as jobs, safety or relatives already there.
intervening opportunity: An attraction along the way, such as a job offer, that may lead a migrant to stop before reaching the planned destination.
intervening obstacle: Something between the origin and the destination that makes a move harder, such as distance, cost, a border, a sea or rough land.

2.11 Forced and Voluntary Migration

Forced migrants are made to move, as refugees, asylum seekers, internally displaced persons or, in the past, enslaved people. Voluntary migrants choose to move, within a country (internal, rural-to-urban) or abroad, in steps or along chains of relatives, as guest workers, as transnational migrants who keep ties to two countries, or seasonally with herds (transhumance).

Forced migration: people are made to move (enslavement, war, persecution, disaster). Voluntary migration: people choose to move.
Forced types: refugee (crossed a border, granted protection), asylum seeker (asked, waiting), internally displaced person (stayed in the country).
Voluntary types: internal (interregional or intraregional), rural-to-urban, step, chain, guest worker, transnational and transhumance.
Real moves often mix choice and force, so explain the case instead of only naming a type.

people are forced to move they are internally displaced persons they are asylum seekers until a decision, and refugees if protection is granted voluntary migration, often in steps or along chains of relatives

forced migration: Migration in which people are made to move, by enslavement, war, persecution or disaster, and have no real choice to stay.
voluntary migration: Migration in which people choose to move, usually for work, family, study or a better life.
refugee: A person who has crossed an international border to escape danger or persecution and has been recognized as needing protection.
internally displaced person: A person forced to leave home who stays inside his or her own country.
asylum seeker: A person who has crossed a border and asked for protection as a refugee but has not yet received a decision.
chain migration: Migration in which people follow relatives or neighbors who moved before them, often to the same place.
step migration: Migration made in stages, such as from a village to a town and then to a large city.
guest worker: A person allowed into another country to work for a set time, who is expected to return home.
transhumance: The seasonal movement of herders and their animals between pastures, such as to mountains in summer and valleys in winter.
transnational migration: Migration in which people keep strong ties to both their country of origin and their new country.
internal migration: Migration within one country. Interregional migration goes between regions; intraregional migration stays within one region.
rural-to-urban migration: Migration from the countryside to cities.

2.12 Effects of Migration

Migration has economic, political, cultural and demographic effects on both the places people leave and the places they go. Origins gain remittances and may lose skills (brain drain) and young adults; destinations gain workers, new foods, languages and religions, and debate immigration policy. Name the place and the scale of every effect.

Remittances are money migrants send home. They raise incomes at the origin but can make families depend on work abroad.
Brain drain is the loss of skilled, educated people from a place, such as doctors and nurses leaving Zimbabwe and Nigeria.
Effects are economic (jobs, wages, remittances), political (debates and laws over immigration), cultural (food, language, religion) and demographic (age and sex structure).
Every effect has a place and a scale: local (a village, a town) and national (a country’s income or laws). Past migrations, such as Irish emigration after 1845, still shape places.

the origin grows older and the destination’s workforce grows they send remittances home, which pay for food, schools and houses the origin suffers a brain drain of skills it paid to train the destination’s culture changes, and its people debate immigration policy

remittance: Money that a migrant sends back to family or community in the place of origin.
brain drain: The loss of educated, skilled people, such as doctors, nurses and engineers, when they move away from a place.