Population Change & Migration (AP Human Geography Unit 2) — Deep Study Notes

Population dynamics

The study of how and why a population’s size changes over time, mainly through births and deaths (and, when included, migration).

Crude Birth Rate (CBR)

Number of live births in a year per 1,000 people in the total population; CBR = (live births ÷ total population) × 1000.

Crude Death Rate (CDR)

Number of deaths in a year per 1,000 people in the total population; CDR = (deaths ÷ total population) × 1000.

Natural Increase Rate (NIR)

Population growth (or decline) from births and deaths only, ignoring migration; NI per 1,000 = CBR − CDR, and NIR(%) = (CBR − CDR) ÷ 10.

Age structure

The distribution of a population by age (and often sex), which can strongly affect crude rates (e.g., many childbearing-age adults can raise CBR; many elderly can raise CDR) even if individual behavior/healthcare is similar.

Demographic Transition Model (DTM)

A model describing typical changes in birth rates, death rates, and overall population growth as societies develop economically and socially (from high rates to low rates).

DTM Stage 1 (High Stationary)

High birth rates and high death rates, resulting in low population growth; associated with pre-industrial conditions, disease, unstable food supply, and high infant/child mortality.

DTM Stage 2 (Early Expanding)

Birth rates stay high while death rates drop rapidly, creating very rapid population growth; driven by sanitation, clean water, basic medical care, vaccination, and improved food supply.

DTM Stage 3 (Late Expanding)

Birth rates decline while death rates decline more slowly or level off; population growth slows but remains positive; linked to urbanization, contraception, female education/workforce participation, and changing norms.

DTM Stage 4 (Low Stationary)

Low birth rates and low death rates, resulting in low or near-zero growth; population change often depends heavily on migration.

DTM Stage 5 (Declining)

Birth rates fall below death rates, producing negative natural increase (natural decrease); associated with very low fertility and aging populations.

Malthusian Theory

Thomas Malthus’s idea that population growth can outpace food production, causing resource shortages and crises such as famine, disease, or conflict (a population vs. resources tension).

Preventive checks (Malthus)

Actions that reduce birth rates (e.g., delaying marriage, having fewer children); they act “before” births to limit population growth.

Positive checks (Malthus)

Events that increase death rates (e.g., famine, disease, war) when population pressure becomes too great.

Push factors

Conditions that drive people to leave an origin location (e.g., unemployment, conflict, persecution, environmental hazards).

Pull factors

Conditions that attract people to a destination (e.g., jobs, safety, political freedom, family networks).

Intervening obstacles

Barriers that make migration harder or alter destination choice (e.g., travel cost, border enforcement/visa rules, language barriers, lack of information).

Chain migration

Migration pattern in which people follow family/community members who migrated earlier, using their networks for housing, job leads, and support—creating persistent origin–destination corridors.

Remittances

Money migrants send back to their origin households/communities; can raise incomes and fund education or small businesses.

Brain drain

Loss of skilled workers from an origin area due to out-migration (e.g., doctors, engineers, teachers), potentially weakening services and slowing development.

Voluntary migration

Movement chosen by the migrant (even if options are constrained), often for jobs, education, family reunification, or lifestyle/amenities.

Forced migration

Movement compelled by threats to life, freedom, or survival (e.g., war, persecution, disasters, development-induced displacement), where staying is not realistically safe.

Refugee

A person who flees their country due to a well-founded fear of persecution (often linked to race, religion, nationality, political opinion, or social group) and seeks safety in another country.

Internally Displaced Person (IDP)

A person forced to leave home but who remains within their country’s borders (does not cross an international boundary).

Asylum seeker

A person who has left their home country and is requesting legal protection in another country; their claim has not yet been fully decided.