Unit 2 Notes: Population Distribution and Composition (AP Human Geography)

Population distribution

The geographic pattern of where people live across Earth’s surface and how settlement is arranged in space.

Population density

A measure of how many people live in a given area; indicates “how crowded” a place is.

Population concentration

How unevenly a population is spread over space (e.g., most people living in a small portion of a country).

Ecumene

The portion of Earth’s surface that is permanently inhabited; areas outside it tend to have major physical constraints.

Arithmetic density

Total population divided by total land area; useful for comparing overall crowding but treats all land as equally usable.

Physiological density

Total population divided by arable (farmable) land area; used to estimate pressure on farmland.

Agricultural density

Number of farmers divided by arable land area; often used to infer agricultural efficiency/technology levels.

Clustered (nucleated) distribution

A settlement pattern where people live close together, often around jobs, services, water, or transportation nodes.

Dispersed distribution

A settlement pattern where people are spread out, often in rural areas with large farm lots or plentiful land.

Linear distribution

A settlement pattern that follows a line such as a coast, river valley, road, or ridge.

Agglomeration

The benefits that firms and people gain by clustering, such as shared labor pools, supplier networks, and knowledge spillovers.

Regional inequality

Uneven development where investment and opportunity concentrate in core regions while peripheral regions lose jobs and/or population.

Urban sprawl

Low-density urban expansion that increases land consumption, car dependence, and habitat fragmentation.

Carrying capacity

The number of people an area can sustainably support given resources, technology, and consumption patterns.

Overpopulation (AP Human Geography)

A condition where population exceeds the capacity of available resources and technology at a desired standard of living (not just “a lot of people”).

Population composition

The characteristics of a population—especially age and sex structure—used to predict future needs and challenges.

Population pyramid (age-sex pyramid)

A graph showing a population’s age cohorts by sex (males typically left, females right) to reveal structure and growth patterns.

Age structure

The proportion of a population in different age groups, often linked to demands for schools, jobs, or elder care.

Cohort

A group of people sharing an age range (e.g., ages 0–4, 5–9) used to analyze population structure.

Sex ratio

The number of males per 100 females; can be shaped by migration, conflict, mortality differences, or cultural practices.

Dependency ratio

An estimate of the burden on the working-age population: (ages 0–14 + 65+) divided by ages 15–64, times 100.

Population momentum

Continued population growth that occurs because a large cohort is entering childbearing years, even if birth rates fall.

Expansive population pyramid

A pyramid with a wide base that narrows quickly; indicates high birth rates, a youthful population, and rapid growth.

Stationary population pyramid

A more rectangular pyramid with relatively balanced cohorts; suggests slower growth and stable planning needs across ages.

Constrictive population pyramid

A pyramid with a narrow base and relatively larger middle/older cohorts; indicates low birth rates, aging, and possible decline.