Population projection

What is population projection?

Population projection deals with computations of future projection size and characteristics based on assumptions about future trends in fertility, mortality and migration.  Since it is not possible to predict the future trends in fertility, mortality and migration with cent percent certainty, it is also not possible to predict the future size and characteristics of a population accurately. Projections are merely intelligent exercise as to what would happen to current population under specified assumptions of fertility, mortality and migration in future years.
Town Planning requires a fair idea of future for which planning needs to be done. For this purpose planners use various methods and tools for “predicting” the future which generally involves population data and population projection as people are the ones who need to be kept in mind and they are the ones for whom planning is done.

Population projection for an area
Population projection for an area

Important uses of population projection:

  • Development Planning like housing, employment etc.
  • Projection of labor force for estimating the future production of goods and services.
  • Population Projections by age for requirement of future school enrolments. This will enable planning of investments in school buildings, teacher training and production of educational material.
  • Future demand for food, power, water, transport etc.
  • Projections of the future age and sex composition of the population are essential for estimating the incidence and prevalence of various diseases and planning for the number of hospitals, hospital beds and specialized facilities as well as training programmes for medical specialists.
  • Future consumption requirement of various goods and services by the population can be obtained from the projection of population by age and sex, in different socio-economic strata. For example, the future demand of feeding bottle for children will depend on the projected number of children in future.

After every census, an Expert Committee/Technical Group under the chairmanship of the Registrar General, India is constituted by the Planning Commission to have the fresh projections based on the latest census data and the levels of fertility and mortality as revealed by the Sample Registration System (SRS).

Its use may vary from country to country as per requirement of town planning and town planning schemes.


  • The method is simple and easily understandable.
  • For projecting the population of a small town the arithmetic progression method is most useful.
  • It is based on the past trend, that is why giving more accurate result.
  • For small term purpose this method gives the most appropriate result.


  • The projection method does not consider any external inputs and project the population on the past trend basis.
  • This is not useful for any city or metropolitan area’s population projection.

Difference between population projection & population forecast:

Forecast has an element of prediction into the near future using current data and sophisticated instruments. Population projection on the other hand, are usually carried out based on a number of alternative assumptions based on trends of growth and other linked factors like future policy of the government, attitude of people etc.

A forecast is based upon assumptions reflecting the conditions the business expects to exist and the course of action reasonably expected to be followed.   A forecast can utilize a specific monetary amount or a reasonable range based on the various assumptions in place.

Methods of Population Projection

There are number of Population projection methods but the widely used & important methods include component method and mathematical method.

I.          Component method:

Procedures, which take the components of the population change into account individually are known as component method for projecting the population.

The basic formula for the component method is:

Pt = P0 + B – D + I – E


Pt  is the population at the later date
Pis the population at the earlier date
B is the number of births occurring between the two dates
D is the number of deaths occurring between the two dates.

Component method is used in India for making projections of major states (states having population of 10 million and above as per the latest census).

I (immigration) is the number of migrants arriving in the population between the two dates.

E (emigration) is the number of emigrants departing from the population between the two dates.   

                    Chief advantage of the component method is that it provides estimates of the future population by age and sex as well as of total figure.

Data required for projections by Component Method

  • Base population and age distribution.
  • Estimates of fertility, mortality and migration at base period.
  • Sex ratio at birth.
  • Assumptions regarding future trends in fertility, mortality and migration.

II.          Mathematical method of projection. An example

The population of country X in 1950 = 25,791,017

The population of country X in 1960 = 34,923,129

The population estimate of country X in 1958 = ?

Difference between population of X in 1950 and   1960, that is,

P1960 – P1950 = 34, 923, 129- 25,791,017

In 10 years, the difference is 9,132,112

In 8 years (1958), the difference will be 9, 132, 112 *0.8   =  7,305,690

Population estimate in 1958 = P1950 + 7,305,690 =  33,096,707. This is Arithmetic Interpolation.

Difference between Component Method and Mathematical Method

Demographers make use of a wide variety of techniques  for preparing population estimates and projections. Most detailed methods for getting estimates and projections treat each of the major components of population change separately and are referred to as Component Method.

Strictly mathematical methods do not do this. These simply project the population based on past growth performance.

Mathematical methods are less reliable than component method.

Read about: Delineation of Formal Region, Delineation of Functional Region, National Urban Information System (NUIS)