# 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

Arithmetic Increase method

• Pn = P + nC
• Here
• P = P2001 = 74638
• C = X = 8301
• So Pn = 74638+ 4 X 8301
• Pn = 107842 People

Geometrical Increase Method

• Pn = P (1+ Ig/100)^n
• Here
• Ig = (19.10×56.02×8.26×15.33×17.72×10.03)^(1/5) = 29.95%
• So Pn = 74638 (1+29.95/100)^4
• Pn = 212846 People

Incremental increase Method

• Pn = P+ n.X + {n (n+1)/2}.Y
• Pn = 74638+ 4×8301 + {4 (4+1)/2}x413
• Pn = 111972 People

CIVIL ENGINEER
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