Table of Contents

Population Forecasting

Population forecasting is a method by which we calculate the future population of any city or region at the interval of n number of decade (10 year) years.

Why we calculate ?

The engineering structure( like canal, water tank, dam, sewer lines, road and highways etc) is build for a usable period of atlest 20 to 50 years, so we calculate the approx population of city on the end of period so that we easily provides the benefit of developing structure.

Factor affecting Population Growth

Increase due to birth
Decrease due to death
Increase due to migration
Economic Factor: The increase and development of new industries will increase the labour population.
Development Program: The increase in the road, canal etc
Social facilities : people attracted by the place where the Hospitals, Educational facility easily available.
communication links : The city which have available facility in interlinking of more cities.
Tourism : The famous place and historical place have a number of tourist all the time.
Natural hazard free: The place where minimum number of earthquake, flood, variation in temperature happen, is a chance that there will be increase in the population.

Population Forecasting Methods

ARITHMETICAL INCREASE METHOD
GEOMETRICAL INCREASE METHOD
INCREMENTAL INCREASE METHOD
GRAPHICAL METHOD
COMPARATIVE GRAPHICAL METHOD
MASTER PLAN METHOD
LOGISTIC CURVE METHOD

ARITHMETICAL INCREASE METHOD

Simplest method
This method is Used for calculation of population of large cities, which having constant development.
Not used for small cities, because it gives lower value.
In this method we consider that the rate of change of population (dP/dt = C) of a city is approximately constant C.

Formula

Pn = P + nC

Here Pn = Population of city after n number of period

P = Current Population

n = number of decade(10 year)

C = average Constant rate of change of population depends upon last 3 to 4 decades.

GEOMETRICAL INCREASE METHOD

The increase rate of population is not constant in this method, the percentage increase in population is considered.
This method is suitable for small cities or new developing town for a few decade years, because it gives higher value by percent increase.

Formula

Pn = P (1+ Ig/100)^n

Ig = average percentage increase per decade

INCREMENTAL INCREASE METHOD

This method is the combination of arithmetic increase and incremental increase method.

Formula

Pn = P+ n.X + {n (n+1)/2}.Y

Where,

Pn = Population after nth decade

X = Average increase

Y = Incremental increase

Problem

Population of a city as per the census records available is as follows

Census Year	Population
1941	24835
1951	29578
1961	46147
1971	49960
1981	57620
1991	67832
2001	74638

Estimate the population of the city after four decades by Arithmetic increased, Geometrical increase and Incremental increase method ?

Solution:

Census Year	Population	Increase in population X		Percent increase in population	Increamental increase
1941	24835	4743		19.10	11826
1951	29578	16569		56.02	-12756
1961	46147	3813		8.26	3847
1971	49960	7660		15.33	2552
1981	57620	10212		17.72	-3406
1991	67832	6806		10.03
2001	74638
Total		49803		126.47	2063
Average per decade		X = 49803/6 =	8301	21.08	Y = 2063/5 =	412.6= 413