Unit 2: Population and Migration Patterns & Processes

Population geography and migration are fundamental topics in AP Human Geography. This unit covers how populations are distributed across the planet, how they change over time, and the spatial patterns of human movement. Understanding these dynamics helps explain everything from political shifts and economic growth to local land use patterns.

Population Distribution and Density

What is the difference between arithmetic density and physiological density?

Geographers use different measurements of population density to understand the relationship between people and resources.

• Arithmetic Density: This is the most common measure. It is the total number of people divided by the total land area. While simple to calculate, it does not account for whether the land is liveable or farmable.
  • Formula: Total Population / Total Land Area
  • Example: The United States has an arithmetic density of about 35 people per square kilometer, which makes it look sparsely populated overall.
• Physiological Density: This is the total number of people divided by the total area of arable land (land suitable for agriculture). This is a much more useful measure of pressure on the environment and food security because it shows how many people must be fed by each unit of farmable land.
  • Formula: Total Population / Arable Land Area
  • Example: Egypt has a low arithmetic density overall, but its physiological density is extremely high (over 2,000 people per square kilometer of arable land) because almost the entire population is concentrated along the narrow, fertile Nile River Valley.

What is agricultural density?

Agricultural Density measures the efficiency of a country’s farming system by comparing the number of farmers to the amount of arable land.

• Formula: Total Number of Farmers / Arable Land Area
• Developed vs. Developing Patterns: Developed countries (like the US or Germany) have very low agricultural densities because they utilize mechanization, high-yield seeds, and advanced technology, allowing a small number of farmers to work massive tracts of land. Developing countries (like Bangladesh or Ethiopia) have high agricultural densities because they rely heavily on manual subsistence farming, requiring many families to farm small plots of land.

Demographic Patterns and the DTM

What is the difference between crude birth rate and crude death rate?

• Crude Birth Rate (CBR): The total number of live births in a year for every 1,000 people alive in the society.
• Crude Death Rate (CDR): The total number of deaths in a year for every 1,000 people alive in the society.
• Note: The term “crude” is used because these measures do not account for the age or sex structure of the population. A country with a large elderly population might have a higher CDR than a country with a younger population, even if health conditions are identical.

What is the rate of natural increase (RNI)?

The Rate of Natural Increase (RNI) represents the percentage by which a population grows or shrinks each year, excluding migration.

• Formula: (CBR - CDR) / 10
• Interpretation: If a country has a CBR of 20 and a CDR of 8, the natural increase is 12 per 1,000, or an RNI of 1.2%. If the result is negative, the population is experiencing natural decrease.

What is doubling time and how is it calculated?

Doubling Time is the number of years needed to double a population, assuming a constant rate of natural increase. It is calculated using the Rule of 70:

• Formula: 70 / RNI (using RNI as a percentage, e.g., 1.2, not 0.012)
• Example: If a country has an RNI of 2.0%, its population will double in approximately 35 years (70 / 2 = 35).

The Demographic Transition Model (DTM)

What is the Demographic Transition Model (DTM)?

The Demographic Transition Model (DTM) is a structural model that describes how a country’s population changes as it develops economically. It maps the transition from high birth and death rates to low birth and death rates over five distinct stages.

Stage 1: High CBR, High CDR -> Low Growth
Stage 2: High CBR, Falling CDR -> High Growth (Industrialization/Medical Revolution)
Stage 3: Falling CBR, Low CDR -> Moderate Growth (Urbanization, education of women)
Stage 4: Low CBR, Low CDR -> Zero Growth / Stabilization
Stage 5: Very Low CBR, Low CDR -> Negative Growth (Declining Population)

What are the 5 stages of the Demographic Transition Model?

Stage 1: Low Growth (High Stationary)

• Characteristics: Very high birth rates and very high, fluctuating death rates. Natural increase is close to zero.
• Causes: Lack of modern medicine, poor sanitation, frequent famines, and agricultural societies where children are needed for manual labor.
• Modern Examples: No entire country is in Stage 1 today, though isolated tribal societies in remote rainforests may fit this profile.

Stage 2: High Growth (Early Expanding)

• Characteristics: Birth rates remain high, but death rates plummet. RNI spikes, leading to rapid population growth.
• Causes: The Industrial Revolution (historic Europe) and the Medical Revolution (developing world mid-20th century). Improved sanitation, clean water, and basic healthcare drastically lower infant mortality.
• Modern Examples: Sub-Saharan countries like Niger, Uganda, and Afghanistan.

Stage 3: Moderate Growth (Late Expanding)

• Characteristics: Birth rates begin to fall rapidly, while death rates continue to decline slowly. Population growth continues but at a slower rate.
• Causes: Urbanization (children become economic liabilities rather than assets in cities), increased access to birth control, and rising education and employment opportunities for women.
• Modern Examples: Mexico, India, and Colombia.

Stage 4: Low Growth (Low Stationary)

• Characteristics: Low birth rates and low death rates. The RNI approaches zero (Zero Population Growth - ZPG).
• Causes: Highly urbanized societies, high levels of female literacy and workforce participation, and family planning is widely accepted.
• Modern Examples: United States, China, and Argentina.

Stage 5: Declining (Negative Growth)

• Characteristics: Birth rates fall below death rates, leading to a natural decrease in population. The population is rapidly aging.
• Causes: Extreme urbanization, career-focused lifestyles, high costs of living, and lack of pro-natalist policies.
• Modern Examples: Japan, Germany, and Italy.

The Epidemiological Transition Model

What is the Epidemiological Transition Model?

Developed by Abdel Omran, the Epidemiological Transition Model (ETM) explains the distinct causes of death that occur in each stage of the Demographic Transition Model.

• Stage 1: Pestilence and Famine: Infectious and parasitic diseases are the primary causes of death. Malthusian checks like bubonic plague and crop failures wipe out large portions of populations.
• Stage 2: Receding Pandemics: Improved sanitation, nutrition, and medicine reduce the spread of infectious diseases. Cholera outbreaks are mapped and contained, and pandemics decrease.
• Stage 3: Degenerative and Human-Created Diseases: Infectious deaths decrease, and chronic illnesses associated with aging become prevalent. Examples include cardiovascular disease and cancer.
• Stage 4: Delayed Degenerative Diseases: Medical advancements extend life expectancy. Major operations, bypass surgeries, and chemotherapy delay deaths from heart disease and cancer.
• Stage 5: Re-emergence of Infectious Diseases: Drug-resistant strains of microbes, increased global travel, and poverty lead to the potential return of infectious diseases (e.g., Malaria, tuberculosis, or new pandemics).

Population Pyramids

What is an age-sex (population) pyramid and how do you read one?

A Population Pyramid is a bar graph that shows the distribution of a population by age groups and sex. The graph is split down the middle: males are displayed on the left, females on the right. The shape of the pyramid tells a geographer which DTM stage a country is in and highlights key historic events.

• Wide Base (Triangle): Indicates rapid growth. High birth rates and a large percentage of youth. Typical of Stage 2 countries (e.g., Niger).
• Gently Sloping Sides (Beehive): Indicates moderate growth. Birth rates are declining. Typical of Stage 3 countries (e.g., Mexico).
• Straight Sides (Column): Indicates slow/stable growth. Even distribution across age brackets. Typical of Stage 4 countries (e.g., United States).
• Narrowing Base (Urn): Indicates population decline. Birth rates are very low, and the elderly population is larger than the youth. Typical of Stage 5 countries (e.g., Japan).

Common Pyramid Anomalies to Look For:

• A “bulge” in the middle-aged cohort: Often indicates immigration (typically young male guest workers, e.g., UAE) or a historic baby boom.
• A “slice” or indent in a specific age range: Usually indicates a war, famine, or major epidemic that occurred when that cohort was young, or a decline in births due to a historical crisis.

Malthusian Theory

What is Thomas Malthus’s population theory?

In 1798, English economist Thomas Malthus published his essay warning that the world’s population growth would eventually outpace its food production capacity, leading to mass famine and social collapse.

• Population Growth: Grows exponentially (geometric progression: 2, 4, 8, 16, 32…).
• Food Production: Grows arithmetically (linear progression: 1, 2, 3, 4, 5…).
• Malthusian Catastrophe: The point where population exceeds food supply, triggering “positive checks” (famine, war, disease) and “preventative checks” (moral restraint, delayed marriage) to force the population back down.

What is the difference between Malthusian and anti-Malthusian perspectives?

• Neo-Malthusians: Argue that Malthus was correct, but that his theory needs updating. They argue that Malthus did not foresee how global resource depletion goes beyond just food. They point to the scarcity of clean water, arable land, and fossil fuels under the pressure of billions of people.
• Anti-Malthusians (Cornucopians / Boserupians): Argue that Malthus failed to foresee major agricultural advancements. Ester Boserup proposed that population growth acts as a stimulus for technological innovation (“necessity is the mother of invention”). The Green Revolution, GMOs, and mechanized agriculture proved that food production could scale exponentially alongside population.

Population Policies

What are examples of pro-natalist and anti-natalist policies?

Governments use demographic policies to influence fertility rates and shape population structures.

• Pro-natalist Policies: Designed to encourage citizens to have children to combat aging populations and declining workforces.
  • Examples: Subsidized childcare, tax breaks, paid parental leave, and cash payouts (e.g., France’s “family allowances” or Singapore’s baby bonus).
• Anti-natalist Policies: Designed to decrease fertility rates and slow rapid population growth.
  • Examples: China’s historic One-Child Policy (fines, career penalties for violators), state-subsidized contraception, and advertising campaigns promoting smaller family sizes (e.g., India’s “Hum Do, Humare Do” campaign).

Migration Patterns and Processes

What are push and pull factors of migration?

Migration is driven by forces that either drive people away from their origin or attract them to a destination.

• Push Factors: Negative conditions at home that force people to leave.
  • Examples: War, political persecution, natural disasters, unemployment, high crime, or famine.
• Pull Factors: Positive conditions at a destination that attract people.
  • Examples: Job opportunities, higher wages, political freedom, safety, better education, and pleasant climates.

What is Ravenstein’s Laws of Migration?

In the 1880s, Ernst Ravenstein proposed a set of general “laws” regarding the migration patterns of humans:

1. Most migration is short-distance: Migrants tend to travel only a short distance to nearby towns or cities (due to distance decay).
2. Migration occurs in steps: Long-distance migrants proceed by steps, moving from villages to small towns, then to larger regional hubs.
3. Long-distance migrants choose big cities: If migrants do travel long distances, they usually target major economic centers.
4. Urban residents migrate less than rural ones: Rural populations are more mobile.
5. Every migration flow generates a counter-flow: When people migrate out of an area, another group moves in (though usually in smaller numbers).
6. Families are less likely to migrate internationally than young adults: Young, single adults historically make up the majority of international migrants.

What is the gravity model of migration?

The Gravity Model predicts the volume of interaction (including migration) between two places. It states that migration is directly related to the population sizes of the two cities and inversely related to the distance between them.

• Concept: Large cities exert a stronger “pull” on migrants than smaller towns, even if the distance is greater. A migrant from a small town in Texas is more likely to migrate to Chicago than to a closer, smaller city in Oklahoma.

What are intervening obstacles and intervening opportunities in migration?

• Intervening Obstacles: Environmental, political, or economic barriers that hinder or block migration.
  • Examples: Mountain ranges, oceans, strict border control policies, visa requirements, or the high financial cost of travel.
• Intervening Opportunities: A positive circumstance encountered along a migration route that causes the migrant to settle down before reaching their original planned destination.
  • Example: A migrant traveling from Central America to New York finds a good-paying job and affordable housing in North Carolina and decides to stop there instead.

Types of Migration

What is the difference between voluntary and forced migration?

• Voluntary Migration: The migrant chooses to move, typically driven by economic pull factors (e.g., moving to another country for a better job).
• Forced Migration: The migrant has no choice but to move due to threats to their survival, such as political violence, war, or environmental disasters (e.g., Syrian refugees fleeing civil war).

What is a refugee vs. an internally displaced person (IDP)?

Both are forced migrants, but they differ in legal status:

• Refugee: A person who has been forced to flee their country due to persecution, war, or violence and has crossed an international border. They are protected under international law.
• Internally Displaced Person (IDP): A person who has been forced to flee their home for the same reasons as a refugee, but remains within their own country’s borders (e.g., people displaced from Florida to Georgia during a hurricane). They do not have the same international legal protections.

What is chain migration?

Chain Migration occurs when people migrate to a specific location because relatives or members of the same nationality previously settled there. The early migrants write letters, send money home, and help new arrivals find housing and work, creating a “chain” of migration that results in cultural clusters (like Little Italy or Chinatown).

What is step migration?

Step Migration is the gradual movement of a migrant in a series of shorter stages. Instead of moving directly from a rural farm to a massive global metropolis like Tokyo, the migrant moves first to a local village, then to a regional town, and finally to the capital city.

What is internal vs. international migration?

• Internal Migration: Movement within a single country’s borders.
  • Interregional: Movement from one region to another (e.g., Rust Belt to Sun Belt in the US).
  • Intraregional: Movement within the same region (e.g., moving from an urban center to a suburb).
• International Migration: Movement across international borders, from one country to another.

Unit 2 Practice Questions

Test your understanding of these Unit 2 concepts with these quick multiple-choice review questions.

Question 1

A country has a Crude Birth Rate (CBR) of 34 and a Crude Death Rate (CDR) of 9. What is its Rate of Natural Increase (RNI)? A) 25%
B) 2.5%
C) 0.25%
D) 4.3%

Question 2

Which of the following population densities is the most useful measure of a country’s food security and resource pressure? A) Arithmetic density
B) Agricultural density
C) Physiological density
D) Economic density

Question 3

According to the Demographic Transition Model (DTM), during which stage does population growth spike due to plummeting death rates combined with persistently high birth rates? A) Stage 1
B) Stage 2
C) Stage 3
D) Stage 4

Question 4

An intervening obstacle is best defined as: A) A positive economic opportunity that stops a migrant along their journey
B) An environmental, political, or economic barrier that halts or complicates migration
C) The pull factor that originally initiated the migration decision
D) The laws of migration formulated by Ernst Ravenstein

Answer Key

1. B — (34 - 9) / 10 = 25 / 10 = 2.5%.
2. C — Physiological density divides total population by arable land, showing the pressure on food production.
3. B — In Stage 2, medical and sanitary advancements drop death rates, but birth rates remain high, yielding rapid growth.
4. B — Intervening obstacles are physical or political barriers that make migration difficult.

Need to memorize the locations of countries experiencing different stages of the Demographic Transition Model? Head over to our homepage to play Border Run and test your knowledge of political boundaries, or try Hidele to practice reading demographic clues and pinpointing secret countries!