AP Human Geography Population and Migration Patterns and Processes — Worked Answer Explanations

Unit 2 · 12 questions explained

Below is a complete answer key for our AP Human Geography Population and Migration Patterns and Processes practice questions. For each question you'll find the correct choice, a full written explanation of how to get there, and — for every wrong answer — a short note on exactly why it's tempting and where it goes wrong. Reading these straight through is one of the fastest ways to find the gaps in a unit before exam day.

Prefer to test yourself first? Take the timed Population and Migration Patterns and Processes practice test and come back here to review, or head back to the Population and Migration Patterns and Processes unit overview.

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Question 1 · Easy
A country has a crude birth rate (CBR) of 12 per 1,000 and a crude death rate (CDR) of 9 per 1,000. Its rate of natural increase (RNI) is:
- A
  0.3% per yearCorrect
- B
  3% per year
  Why not B: RNI = (CBR – CDR) / 10, expressed as a percentage. (12 – 9) = 3 per 1,000, which is 0.3%, not 3%.
- C
  21 per 1,000
  Why not C: 21 per 1,000 is the sum of CBR and CDR, not their difference. RNI = CBR − CDR.
- D
  0.03% per year
  Why not D: This is an order-of-magnitude error. (12 − 9) / 1,000 × 100 = 0.3%, not 0.03%.
Explanation
Rate of Natural Increase = (Crude Birth Rate − Crude Death Rate) ÷ 10, expressed as a percentage. Here: (12 − 9) ÷ 10 = 0.3% per year. This figure excludes migration and captures only the balance of births and deaths. An RNI of 0.3% is characteristic of Stage 3 or early Stage 4 in the demographic transition model.

Key takeaway
RNI (%) = (CBR − CDR) ÷ 10. It measures natural population growth, excluding migration.
Question 2 · Easy
A country in Stage 2 of the Demographic Transition Model (DTM) is characterized by:
- A
  High birth rates and high death rates, producing slow population growth.
  Why not A: High birth rates paired with high death rates describes Stage 1, not Stage 2. Stage 2 specifically features falling death rates while birth rates remain high.
- B
  High birth rates and rapidly falling death rates, producing rapid population growth.Correct
- C
  Falling birth rates and low death rates, producing slow population growth.
  Why not C: Falling birth rates paired with low death rates describe Stage 3, when fertility begins declining in response to industrialization and urbanization.
- D
  Low birth rates and low death rates, producing near-zero population growth.
  Why not D: Low birth rates and low death rates characterize Stage 4, the most industrialized stage of the DTM.
Explanation
The Demographic Transition Model describes four stages of population change. Stage 2 begins when improved sanitation, medicine, and food supply drive death rates downward while birth rates remain high — reflecting cultural norms and agricultural labor demands. The gap between the two rates creates a population explosion. Many sub-Saharan African nations were in Stage 2 during much of the 20th century.

Key takeaway
Stage 2 DTM: death rates fall (sanitation, medicine) while birth rates stay high, causing rapid population growth.
Question 3 · Easy
An age-sex pyramid with a wide base, narrow middle, and very narrow apex most likely represents a country with:
- A
  Low fertility, low mortality, and an aging population.
  Why not A: Low fertility and aging populations produce a pyramid with a narrow base and wider middle/top — often called a barrel or inverted pyramid shape.
- B
  High fertility, high mortality, and a youthful population.Correct
- C
  Net in-migration of working-age adults from neighboring countries.
  Why not C: Net in-migration of working-age adults creates a bulge in the working-age cohorts (20–45), not a uniformly wide base.
- D
  A post-industrial economy with high immigration and low emigration.
  Why not D: Post-industrial economies typically have aging populations with narrow bases; high immigration might widen working-age bands but not the broad-base pattern.
Explanation
An age-sex pyramid with a wide base and narrow apex indicates that the population has many young people and relatively few older adults. This pattern occurs where fertility is high (many children born) and mortality is also high (many people die before reaching old age), typical of Stage 1 or Stage 2 on the DTM. Countries in Sub-Saharan Africa commonly display this pyramid shape.

Key takeaway
Wide-base, narrow-apex pyramid = high fertility + high mortality = youthful population (DTM Stage 1 or early Stage 2).
Question 4 · Easy
Ravenstein's Laws of Migration include the observation that most migrants move only short distances and that migration occurs in a series of steps. A rural villager moves first to a nearby small town, then to a regional city, and finally to a national capital. This pattern best illustrates:
- A
  Forced migration, driven by environmental disasters in the rural area.
  Why not A: Forced migration is driven by involuntary push factors such as conflict or disaster, not by a voluntary, incremental ladder of moves to progressively larger cities.
- B
  Chain migration, in which later migrants follow the path of earlier migrants from the same origin.
  Why not B: Chain migration describes social networks linking migrants from the same origin to a specific destination; it is not about a single person's step-by-step movement up an urban hierarchy.
- C
  Step migration, in which migrants move progressively to larger and more distant destinations.Correct
- D
  Cyclic movement, in which individuals return to their origin after a period away.
  Why not D: Cyclic movement (commuting, seasonal migration) involves a return to the origin; step migration involves a permanent progressive relocation toward larger urban centers.
Explanation
Ravenstein observed that rural-to-urban migrants rarely leap directly to a distant major city. Instead, they often move in stages — from village to town to city to metropolis — gradually improving economic opportunities and social networks at each step. This step migration pattern is consistent with Ravenstein's law that most migrants move only short distances at a time, building knowledge and connections before larger moves.

Key takeaway
Step migration: migrants move progressively through a hierarchy of places (village → town → city) rather than directly to a distant destination.
Question 5 · Easy
A Syrian refugee family flees to Turkey due to civil war in their home country. This movement is best classified as:
- A
  Voluntary migration driven by pull factors in Turkey.
  Why not A: Voluntary migration is motivated by choice, not by fear for one's safety. Fleeing active conflict is not a voluntary, pull-factor driven decision.
- B
  Forced migration driven by a push factor — armed conflict in the origin country.Correct
- C
  Step migration, in which the family is moving progressively toward a wealthier destination.
  Why not C: Step migration describes a pattern of incremental moves up an urban hierarchy; it is not a classification of whether migration is voluntary or forced.
- D
  Circular migration, in which workers regularly move back and forth between two countries.
  Why not D: Circular migration is a cyclical, often voluntary pattern of seasonal or labor migration; fleeing conflict is a one-direction forced displacement.
Explanation
Forced migration occurs when people are compelled to leave their homes by factors beyond their control — armed conflict, persecution, natural disaster, or government coercion. In this case, civil war is a powerful push factor driving the family out of Syria. The UN classifies people fleeing persecution or conflict as refugees, a legal category under the 1951 Refugee Convention. This differs from economic migrants who move voluntarily in search of better opportunities.

Key takeaway
Forced migration is driven by involuntary push factors (conflict, persecution, disaster) that leave migrants no safe alternative but to flee.
Question 6 · Medium
A geographer studying population density finds that a country's arithmetic (crude) density is 300 people per km², but its physiological density is 1,200 people per arable km². What does the high physiological density suggest about this country?
- A
  The country has a large total land area relative to its population.
  Why not A: Large land area relative to population produces low arithmetic density, not the specific gap between arithmetic and physiological density.
- B
  Only a small fraction of the country's total land is suitable for agriculture, concentrating population pressure on farmland.Correct
- C
  The country has advanced irrigation technology that increases crop yields per hectare.
  Why not C: Irrigation improves yield (agricultural density concept) but does not directly explain the arithmetic-to-physiological gap, which reflects how much land is arable.
- D
  The country is in Stage 4 of the DTM, with low birth rates and an aging labor force.
  Why not D: DTM stage relates to birth/death rates, not to the ratio of arable land to total land area.
Explanation
Physiological density = total population ÷ arable land. When physiological density is much higher than arithmetic density, it means a large share of total land is non-arable (desert, mountains, ice). Egypt is a classic example: most population clusters along the Nile Valley, giving very high physiological density despite vast desert territory that brings down arithmetic density. High physiological density signals potential pressure on food-producing capacity.

Key takeaway
When physiological density >> arithmetic density, most land is non-arable; population is highly concentrated on limited farmland.
Question 7 · Medium
A country's total fertility rate (TFR) drops below replacement level (approximately 2.1 children per woman) while the population continues to grow for several decades. This continued growth is best explained by:
- A
  An increase in the crude death rate as the population ages.
  Why not A: A rising death rate would slow growth further; it does not explain why growth continues despite sub-replacement fertility.
- B
  Population momentum, caused by a large cohort of women of childbearing age from past high-fertility periods.Correct
- C
  Epidemiological transition, which reduces chronic disease mortality among the elderly.
  Why not C: The epidemiological transition affects the types of diseases causing death but does not directly sustain population growth after fertility falls below replacement.
- D
  The demographic dividend, which describes economic growth from a large working-age population.
  Why not D: The demographic dividend describes an economic phenomenon associated with a large working-age cohort; it is not the mechanism that sustains population growth after fertility declines.
Explanation
Population momentum occurs when a country with a previously high TFR transitions to below-replacement fertility. The large generation of women born during the high-fertility era moves into childbearing age and produces many children even at a lower per-woman rate. This inertia sustains absolute population growth for decades after TFR drops below 2.1. China, India, and many other countries experienced population momentum after fertility declined.

Key takeaway
Population momentum: even after TFR falls below replacement, a large cohort of women of childbearing age sustains total population growth for decades.
Question 8 · Medium
According to Ravenstein's Laws of Migration, which of the following patterns would he predict about gender and migration distance?
- A
  Men are more likely to undertake long-distance international migrations; women more commonly migrate shorter distances.Correct
- B
  Women are more likely to migrate internationally while men migrate internally.
  Why not B: Ravenstein's 19th-century observations found the opposite: women predominated in short-distance internal migration; men in longer international moves.
- C
  Gender has no influence on migration distance according to Ravenstein.
  Why not C: Ravenstein explicitly addressed gender differences in his laws, noting that women and men exhibited different distance patterns.
- D
  Rural women migrate farther than rural men because agricultural work pushes them out of rural areas.
  Why not D: Ravenstein's laws identified men as the longer-distance migrants; women, particularly in the 19th century context he studied, more commonly moved locally.
Explanation
Ravenstein's Laws (1885–1889) included the observation that females are more migratory than males over short distances, while males predominate in long-distance and international migration. This pattern reflected 19th-century labor markets (men seeking industrial or colonial employment abroad) and domestic constraints on women's long-distance movement. Contemporary migration patterns are more complex and vary significantly by region and economic context.

Key takeaway
Ravenstein observed that men are more common in long-distance/international migration; women more common in short-distance internal migration.
Question 9 · Medium
A country experiencing the epidemiological transition shifts from high mortality due to infectious diseases to high mortality due to chronic and degenerative diseases. This shift is most associated with which stage of the Demographic Transition Model?
- A
  Stage 1, when both birth and death rates are high and infectious disease is the leading cause of death.
  Why not A: In Stage 1, mortality from infectious disease is high, but the epidemiological transition describes the shift away from that pattern, which begins in Stage 2.
- B
  Stage 2, when infectious disease mortality begins to decline due to improved sanitation and medicine.
  Why not B: Stage 2 is the beginning of the epidemiological transition (infectious disease mortality declining), but the full shift to chronic disease dominance occurs in Stage 3–4.
- C
  Stages 3 and 4, when infectious disease mortality is low and chronic diseases such as cancer and heart disease become dominant causes of death.Correct
- D
  Stage 5 (hypothetical), when death rates rise above birth rates causing population decline.
  Why not D: Stage 5 (negative growth) concerns the overall birth-death balance; the epidemiological transition to chronic disease dominance is complete by Stage 4.
Explanation
The epidemiological transition, proposed by Abdel Omran, describes how the causes of death shift from infectious/parasitic diseases to degenerative/chronic diseases (heart disease, cancer, stroke) as countries industrialize and improve public health. This transition corresponds to Stages 3 and 4 of the DTM, when death rates from infectious disease have already declined and life expectancy is long enough for chronic conditions to predominate.

Key takeaway
Epidemiological transition: death causes shift from infectious diseases (Stages 1–2) to chronic/degenerative diseases (Stages 3–4).
Question 10 · Hard
The gravity model of migration predicts that the volume of migration between two cities will increase if the population of both cities grows but the distance between them remains constant. This prediction is most directly based on the principle that:
- A
  Larger cities have better infrastructure, which lowers transportation costs over any fixed distance.
  Why not A: Infrastructure costs may change, but the gravity model's core logic is mathematical — it uses population size and distance, not infrastructure quality.
- B
  Migration volume is proportional to the product of both populations and inversely proportional to the distance between them.Correct
- C
  Migration declines as cities grow because competition for housing and jobs reduces attractiveness.
  Why not C: The gravity model predicts migration increases with population size, not decreases. Larger populations generate more potential migrants and more destination opportunities.
- D
  Distance decay does not apply when cities reach a critical population threshold.
  Why not D: The gravity model maintains distance decay at all population levels; larger size increases flow but distance still reduces it.
Explanation
The gravity model, borrowed from Newtonian physics, estimates migration flow as proportional to (Population₁ × Population₂) ÷ Distance². Larger cities generate more potential migrants (origin mass) and attract more migrants (destination mass). Holding distance constant, doubling both city populations would quadruple predicted flow. Distance still reduces flow through a friction effect. The model is widely used to predict trade, commuting, and information flow in addition to migration.

Key takeaway
Gravity model: migration volume ∝ (population₁ × population₂) ÷ distance². Larger cities = more flow; greater distance = less flow.
Question 11 · Hard
A country in Stage 4 of the Demographic Transition Model shows a stationary or slightly declining population. A policy maker proposes encouraging immigration to maintain the working-age population. Which demographic challenge most directly motivates this policy?
- A
  Overpopulation, because Stage 4 countries have too many people relative to resources.
  Why not A: Stage 4 countries have low or negative growth — the concern is labor force shrinkage and pension funding, not overpopulation.
- B
  An aging population and a shrinking dependency ratio of workers to retirees, threatening pension and healthcare systems.Correct
- C
  High infant mortality, which reduces the productive workforce before workers reach employment age.
  Why not C: Stage 4 countries have low infant mortality; this is not a characteristic challenge of this stage.
- D
  Population momentum, which is causing the population to grow too rapidly for economic resources to support.
  Why not D: Population momentum sustains growth after fertility declines; Stage 4 countries have already passed that phase and face the opposite problem of decline or stagnation.
Explanation
Stage 4 nations (typical of Japan, Germany, Italy, South Korea) have very low TFRs and low death rates, producing an aging population. The dependency ratio shifts unfavorably: fewer working-age people must support a growing retiree cohort. This strains pay-as-you-go pension systems and healthcare budgets. Immigration of working-age people is one policy response; others include pro-natalist incentives and raising the retirement age.

Key takeaway
Stage 4 demographic challenge: aging population and shrinking worker-to-retiree ratio threaten pensions and healthcare funding.
Question 12 · Hard
In the context of the push-pull model of migration, which of the following is a pull factor drawing migrants to a destination country?
- A
  Chronic unemployment and low wages in the origin country.
  Why not A: Unemployment and low wages are push factors that drive people away from the origin — they characterize the origin, not the destination.
- B
  Political persecution of ethnic or religious minorities in the origin country.
  Why not B: Persecution is a push factor in the origin country that forces emigration, not an attribute of the destination that attracts migrants.
- C
  Abundant employment opportunities and higher wages in the destination country.Correct
- D
  Environmental degradation and land loss from sea level rise in the origin country.
  Why not D: Environmental push factors drive people away from their origin; they are not pull factors in a destination country.
Explanation
The push-pull model distinguishes between push factors (negative conditions at the origin that drive emigration) and pull factors (positive conditions at the destination that attract migrants). Economic opportunities such as higher wages, available jobs, and upward mobility are classic pull factors. Political stability, quality education, and family reunification are also pull factors. The decision to migrate typically involves both types simultaneously, filtered by personal resources and intervening obstacles.

Key takeaway
Pull factors are positive attributes of the destination (jobs, wages, stability) that attract migrants; push factors are negative origin conditions that drive emigration.