Core global change · Population patterns and development

IB Diploma Programme Geography HL (first assessment 2019; 2017 guide). This topic covers the first unit of the core 核心部分, Changing population, which SL and HL students both study. It has three parts: where people live and why, how populations change, and the challenges and opportunities this brings. Paper 2 tests the core with structured questions, a visual source and an essay. The examiners like calculations from data, so each section below shows one.

In 2024, 9.54 million babies were born in China and 10.93 million people died. The population fell for the third year in a row, to 1.408 billion. Fifty years earlier, China's problem was the opposite: too many births. In one lifetime the country has moved from fast growth to decline. This topic gives you the tools to explain such a change and to judge what governments can do about it.

Must-know for this topic:

Population distribution 人口分布 is the pattern of where people live. It depends on physical factors 自然因素 (climate, water, relief and soil) and human factors 人文因素 (jobs, transport, history and government policy). In China, about 94% of people live east of the "Hu Line", a line drawn from Heihe in the north-east to Tengchong in the south-west, on about 43% of the land. The west is high, dry and cold.

Population density 人口密度 is people per square kilometre:

Dividing by farmland instead of total area gives the physiological density 生理密度, which shows the pressure on the land that grows food.

The same population gives very different densities depending on which land you divide by

People also move towards cities. A megacity 超大城市 has more than 10 million people; there were 33 in 2018 (UN), including Shanghai, Beijing, Chongqing and Guangzhou. Inside a country, a rich, well-connected core region 核心区 (such as the Yangtze River Delta) attracts people, money and ideas from a poorer periphery 边缘区.

A TFR of about 2.1 is the replacement level 更替水平: each generation just replaces itself. China's TFR is about 1.0; Niger's is about 6.

Worked example. A country has a CBR of 24 and a CDR of 8 per 1,000.

• Natural increase = 24 − 8 = 16 per 1,000 = 1.6% a year.
• Doubling time 倍增时间 ≈ 70 ÷ growth rate in % = 70 ÷ 1.6 ≈ 44 years.

Total change also includes net migration 净迁移: people arriving minus people leaving.

China's births and deaths, 2016–2024: natural decrease began in 2022

From the graph: in 2024, natural change in China was 9.54 − 10.93 = −1.39 million.

The demographic transition model

The demographic transition model 人口转变模型 (DTM) shows how birth and death rates change as a country develops:

Demographic transition: death rates fall before birth rates, and the gap is population growth

The model is based on European history. It does not include migration, and it does not say how long each stage lasts: China passed through stages 2 to 4 in about 50 years, much faster than Britain.

Population pyramids and dependency

A population pyramid 人口金字塔 shows the number of males and females in each age group. A wide base means many young people; straight sides mean similar numbers at each age; a narrow base means few recent births.

A wide base means large young cohorts; straight sides mean similar cohort sizes

The dependency ratio 抚养比 compares people of non-working age with people of working age:

Worked example. A town has 20,000 people aged 0–14, 15,000 aged 65 and over, and 70,000 aged 15–64. Dependency ratio = (20,000 + 15,000) ÷ 70,000 × 100 = 50. Every 100 people of working age support 50 dependants.

When birth rates fall, a country for some years has many people of working age and few dependants. This can speed up growth: the demographic dividend 人口红利. China's fast growth from the 1980s used this dividend; it is now ending.

Ageing populations 人口老龄化 have more older people: Japan had about 29% of its people aged 65 and over in 2023. Problems: fewer workers, more spending on pensions and health care. Opportunities: older people care for grandchildren and volunteer, and "silver" industries grow. Youthful populations 年轻型人口 need schools and jobs; without jobs, young people may migrate or become frustrated.

Governments respond with policies:

Policies on births work slowly. China allowed three children in 2021, but births kept falling, because housing, education and childcare are expensive and many young people marry later. China's sex ratio at birth 出生性别比 was also unbalanced: about 111 boys per 100 girls in the 2020 census, against a natural level of about 105.

Migration 迁移 is a long-term move from one place to another. It can be internal 国内的 or international 国际的, and voluntary or forced.

Push factors at the origin, pull factors at the destination, and intervening obstacles between

Push factors 推力因素 drive people away; pull factors 拉力因素 attract them; intervening obstacles 中间障碍 such as cost, distance and borders stop some people. There were about 280 million international migrants in 2020 (UN). A refugee 难民 has crossed a border to escape persecution or war; an internally displaced person 国内流离失所者 (IDP) has fled but stayed inside their own country.

China has one of the largest internal migrations in history: the 2020 census counted about 376 million people living outside the area where their household is registered, most of them from villages to cities in the east. Under the hukou 户口 system, many migrants could not easily use schools and health care in their new city, which is slowly changing.

Migration has effects on both places:

• Distribution: physical and human factors; the Hu Line; arithmetic and physiological density; megacities; core and periphery.
• Measures: CBR, CDR, natural increase, TFR and replacement level 2.1; doubling time (70 ÷ 1.6 ≈ 44 years); China's −1.39 million in 2024.
• The DTM: five stages with reasons, and two limits.
• Pyramids; the dependency ratio (worked example 50); the demographic dividend.
• Ageing and youthful populations; anti- and pro-natalist policies; the sex ratio at birth.
• Migration: push, pull and obstacles; refugees and IDPs; China's 376 million internal migrants and hukou; effects at origin and destination.