Geography · Ch 2 — The World Population: Distribution, Density and Growth
Components of Population Change
Components of Population Change
The size of a country’s population does not change only because people are born or die. There is a third force at work: migration. Together, births, deaths, and migration are the three components of population change. Each one alters the total number of people in a region, and understanding them is essential to explaining why some populations grow rapidly while others shrink or remain stable.
Births are measured using the Crude Birth Rate (CBR). This is the number of live births in a given year per 1,000 people in the population. The formula is:
CBR = (B ÷ P) × 1000
where B = number of live births during the year, and P = estimated mid-year population of the area. CBR is called ‘crude’ because it does not account for the age or sex structure of the population — it simply gives a raw rate.
Deaths are measured using the Crude Death Rate (CDR). This is the number of deaths in a particular year per 1,000 people in a region. The formula is:
CDR = (D ÷ P) × 1000
where D = number of deaths, and P = estimated mid-year population. Death rate plays an active role in population change: population growth occurs not only when the birth rate rises, but also when the death rate falls. Mortality rates are generally influenced by three broad factors: the region’s demographic structure (age distribution), its level of social advancement (education, healthcare), and its level of economic development.
The textbook includes a figure (Fig. 2.2) showing the Demographic Transition Theory, with three stages — High Fluctuating, Expanding, and Low Fluctuating — and examples such as Bangladesh, Sri Lanka, Canada, Japan, and the USA. This figure illustrates how birth and death rates change over time, but the text does not provide a detailed explanation of the theory in this section.
Migration is the third component. When people move from one place to another, the place they leave is called the Place of Origin, and the place they arrive at is called the Place of Destination. The place of origin experiences a decrease in population, while the place of destination sees an increase. Migration can be interpreted as a spontaneous effort to achieve a better balance between population and resources.
Migration may be:
- Permanent (a person moves and settles permanently)
- Temporary (a person moves for a fixed period)
- Seasonal (movement follows a seasonal pattern, e.g., for harvest work)
It can take place between different types of areas:
- Rural to rural
- Rural to urban
- Urban to urban
- Urban to rural
A key point: the same person is both an immigrant and an emigrant. A migrant who moves into a new place is called an immigrant; a migrant who moves out of a place is called an emigrant.
Why do people migrate? The fundamental reason is the search for a better economic and social life. The factors that drive migration are divided into two sets: …