Population is the total number of people; old, young men and women living in a particular place, area, city and country at a given period of time.

     Population census is the official head count of all the people of a given country. It is usually carried out every ten years in Nigeria.

Definition of terms

1. Birth rate: This is the total number of birth per thousand of people in a particular year

2. Death rate: It is the total number of death per population in a year.

3. Migration: It is the movement of people between regions or country at the e. Inflow and outflow of people from one place to another.

4. Immigration: It is the movement of people into a country. Such people are referred to as immigrants.

5. Immigration: The movement of people f on their country to another country. Such people are referred to to emmigrants

6. Net migration : It is the difference between the immigrants and emmigrants.



This refers to how people are spread over a geographical area system some area are densely populated why some are sparsely populated. Factors responsible for geographical distribution of a population include:

Topography and climate condition

Commercial and industrial activities

Availability of natural resources

Natural disaster

Age distribution

this is the breakdown of a population into age groups. It can also be described as the spread of ages within a population. Areas within the population can be grouped as follows:

  • 0-18 years infants
  • 19-65 years working population
  • 65 years and above elderly or aged
  • OR
  • 0-5 years preschool age
  • 6-11 years primary School age
  • 12-16 years secondary school or post primary age
  • 17-21 years post secondary school age
  • 22-60 years working population of active population
  • 60 and above aged and elderly
  • OR
  • 0-18 dependent children
  • 18-60 years working active population
  • Over 60 years(bracket open dependents old people)


This is the ratio of dependent population to the working population


Dependent Population/Working population                                                                                       


 This is the distribution of a population by gender or sex either male or female. The major importance of this is that it enables the government to determine the sex ratio of a population. i.e. Sex ratio= male:female


This is the distribution of a population into the type of jobs or occupation of the people in the population. The division could be based on the skill needed on the job i.e. 

Skilled labour

Semi-skilled labour

Unskilled labour


A country is described as overpopulated if the resources are insufficient to meet the aggregate demand. Standard of living is poor as the few available goods and services are to be shared out among many people. Its population is so great that an increase in population would lead to a decrease in output per head (law of diminishing returns

A country is described as underpopulated if there are insufficient people to make full use of the existing resources. An increase in population would lead to an increase in output per head (closer to optimum population). They have more resources than the needs of the existing population. Their standards of living are high

As the size of the population in a country grows, they are able to produce more and more, but after a point there will be diminishing returns as there are too many people and too few resources- output per head will fal

Optimum Population 

Optimum population is where the amount of resources available in a country is equal to the country’s population, so there are enough resources to maintain its population 


  • It is the most efficient level of population where output per head is maximize
  • The economy will be sustainable and   
  • Achieving optimum population
  • Social and Cultural: change religious views and give women more right
  • conomic: increasing job opportunities, providing education and career prospect
  • Medical and Scientific: sexual education and contraception should be made availabl
  • Political: improve education to direct people into a caree

Population Pyramid

The structure of a population pyramid shows the

  • gender distribution
  • age distribution
  • name of the country
  • year of census

Population ageing is a phenomenon that occurs when the median age of a country or region rises due to rising life expectancy and/or declining birth rates

Countries with high ageing population may have the following implications

  • labour availability but unemployment 
  • economic growth
  • size and nature of market
  • dependency ratio
  • welfare service
  • housing market

Population Structure

Developing countries often have high birth rate and high death rate implying a relatively low life expectancy. Each successive age group is smaller than in the preceding age group. Their pyramids often have a wider base and narrower top. Majority of the population works in the primary/secondary sector

Developing countries often have low birth rate and low death rate implying a relatively high life expectancy. Their pyramids often have a narrower base and wider top (generally equal). Majority of the population works in tertiary sector

Population structure depends on

age: dependents, working populatio

gender : male or female

occupation: primary/secondary/tertiary

area: rural or urban

Age Structure

 Age structure refers  to the number of people in each group of the population

Developed countries tend to have an even age structure whereas less developed countries have over half their population aged under 1

The age groups are

  • working age
  • dependents age 
  • ageing population
  • Working Age
  • Contains all the people above 16 and below the retirement ages 65

The working population is made up of all those people who are employees, the self-employed and the unemployed. It consists of all those over the age of 16 who are either in employment or actively seeking employment

It does not include, however, people above or below the working age, students who are studying, the disabled, prisoners and stay at home individual

The size of the working population can be altered by the changes in school leaving age, retirement age and the number of house persons seeking wor

It provides the tax revenue for the government and produces the goods and services required by other groups in society

The activity or participation rate measures the proportion of the population of working age which is in paid employment or currently seeking employmen

Reasons behind Labor Supply Increase

More students are dropping out to seek work

Retirement age is increased so more working life for people

Increase in number of people of working age who decided to join the labor forc

Dependent Age Group

Everyone below the official school leaving age and those above the retirement age .

Any increase in these groups of people means that the people in work have more people to support and the living standards per head will fal

Dependency ratio measures the ratio of those in non-working age groups to those in working age groups

Total Population / Number of People  Workers

Costs of dependents to an economy

  • working people may have to pay more tax to support the dependent
  • country may have to import more to satisfy deman
  • balance of trade may become unfavorable

Consequences of an Ageing Population

  • Changes in demand patterns as there is an increase in demand for commodities required by old people
  • Less flexible and adventurous population- therefore decreasing risk, investment and economic progres
  • An increased burden on the population to produce commodities and provide the taxation to support the older group
  • Older people are less mobile and therefore it will be more difficult to adapt to changes in technology, taste, fashion etc
  • Gender Structure
  • Changes in allocation of resource
  • Different demand
  • Changes in mobility of labour
  • Affect activity rates

Occupation Structure

  • Refers to the proportion of the population employed in different occupation
  • Gradual swing from manual to non-manual occupations due to the decline of the manufacturing industry
  • Workers are increasing in the  industries
  • Large increase in the number of people in part time jobs- especially wome
  • More self-employment as people who are made redundant are able to start businesses themselve
  • Long-term trend is moving towards the expansion of the tertiary sector and decline of the secondary and primary sectors because of mechanisation
  • increased efficiency of robot
  • more capital intensive productio
  • more services are needed to help distribute commodities
  • people demand more services as income and living standards increase
  • female employment is most in the tertiary sector

Area Structure

  • There is an uneven spread of people because industries are in towns but farming areas are not. Some areas are remote.
  • Improved means of transport and increasing congestion may cause people, especially retired people, to shift from the city to the countr
  • Push/pull factors may cause the working population to move to the cities.


This occurs when the size of population is very large in relation to the available resources to support them. This in turn leads to a minimum return per head when the population is matched with existing technology and resources.


This occurs when the number of people in the population has a maximum output per head when compared with existing technology and resources. This is usually the best population size for a country because all resources will be fully utilised.


this occurs when people living in a geographical area and less than existing technology and resources. In such situation, resources will not be efficiently utilised.


population density refers to the number of people within a geographical area per square kilometre. It is calculated as follows

Population density= Total population/Land area.                                                                             

  •    Affecting Population Change

1. Birth Rate:

The crude birth rate is the number of live births per annum per thousand of the population

The infant mortality rate is the number of death of infants in one year per thousand live births in that year.

The factors affecting birth rate are:

  • availability of birth control
  • living standards in terms of quality and quantity decides infant mortality rate
  • custom and religion- some religions do not support birth controls, others think big families are unfashionable
  • female employment: many women in developed countries do not want to break their career to bring up children or support the extra cost
  • number of marriages/ polygamy

2. Death Rate:

The crude death rate is the number of deaths per annum per thousand of the population.

The factors affecting death rate are:

  • standard of living in terms of housing, diet and sanitation
  • medical advances and health care
  • natural disasters/ wars
  • law and order situation
  • awareness about health and safety

3. Migration

Migration happens when people permanently leave one country (emigration) and enter another (immigration)

  • Net migration is the difference between immigration and emigration
  • People usually want to leave countries for two reasons:
  • push factors- unemployment, low standard of living, poor climate in own country
  • pull factors- good job prospects, high living standards of new country

Methods of Calculating Population

Population can increase when:

  • birth rate exceeds death rate
  • immigration exceeds emigration
  • Natural Rate of Increase of Population: Birth Rate- Death Rate
  • Net Migration: Immigrants- Emigrants
  • Total Increase in Population: Natural Increase + Net Migration               

    Mathematical Approach to Population Studies

    Example 1

    The total number of males in a country which has a total land area of 140,000sq Km is 150,000,000 while that of the females is 130,000,000 including all migrants. Calculate
    (a) The total population of the country
    (b) The population density of the country
    (a) Total population = No of males + No of females
    = 150,000,000 + 130,000,000 = 280,000,000 People
    (b) Population Density = Total Population / Land area
    = 280,000,000 / 140,000 = 2,000 persons per sq Km.

    Example 2

    If the population density of Tanko district is 3,500 persons per sq Km, and the total population is 1,400,000 people. Calculate the total land area of Tanko district.
    Land area = Total Population / Population Density
    Land area = 1,400,000 / 3, 500
    Land area = 400 sq Km.
    Some Population Formulae
    Rate of population growth R = Birth rate – Death rate + Net migration
    Net migration = Immigrants – Emigrants
    I.e the difference between the number of immigrants and emigrants is Net migration.
    Natural increase = Birth rate – Death rate
    Percentage Increase = New Population – old Population. × 100
    Old population
    Dependency ratio = Dependent population / Working or independent population.
    Example 3
    Use the information table and answer the following questions

    (a) The natural increase of the population in 1996
    (b) Determine the net migration within the period.
    (c) The rate of growth of the population in 1996
    (d) The population of the country in 1996
    (e) What is the percentage increase in the population of the country from 1980 to 1996
    (a) Natural increase = Birth rate – Death rate
    = 48 million – 12 million = 36 million
    (b) Net migration = Immigrants – Emigrants
    = 10 million – 4 million = 6 million
    (c) Rate of population growth, R = Birth rate – Death rate + Net migration
    = 48 million – 12 million + 6 million = 42 million

    (d) Population of the country in 1996 = 1980 Population + Net migration + Birth rate – Death rate
    = 56 million + 6 million + 48 million – 12 million = 98 million
    (e) Percentage increase from 1980 to 1996
    = New Population – old population. × 100
    Old Population. 1
    = 98 million – 56 million. × 100
    56 million 1
    = 42 million. × 100
    56 million
    = 0.75 × 100
    = 75%
    Example 4
    The pie chart below represents the age of distribution of population. The total population is 240 million.

    From the information above, Calculate:
    (a) The population of children between 0 and 17 years
    (b) The population of old people (60 + years)
    (c) The dependency ratio
    (a) Population of children between 0 and 17 years = 120 × 240
    360. 1
    = 28,800
    = 80 million
    N.B “the 360 is gotten by adding the percentage of each age in the pie chart, i.e 120% + 150% + 90% = 360 and the 240 used is the total population given in the question”.

    (b) Population of old people (60 + years) = 90 × 240
    360. 1
    = 60 million
    (c) working Population (18 – 59 years) = 150 × 240
    360. 1
    = 100 million
    Dependency ratio = Population of children ( 0 – 17 years) + Population of old people (60+ years)
    Working Population (18 – 59 years)
    = 80 million + 60 million
    100 million
    = 140 million
    100 million

    = 1.4 / 1 or 1.4 : 1                                                  


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