population estimation

Sanitary Engineering

Eng: Mohammed S. Yassin 2nd semester , 2009

Population Estimation:

Several methods are used to forecast population in the future (each method has its own

assumption)

Three methods will be discussed (Arithmetic method , Geometric increase method and

saturation method ).

"-Arithmetic method:

Where , : population after time t . Unit :capita

: Present population . Unit: capita

K : increasing rate of population

Unit : (capita/yr)

, Unit : (capita/yr)

R : growth rate

Note: This method has an assumption that the increase in population is constant from year

to year.

Since the rate of change in population is constant, the relation between the time t and the

future population ( ) is linear. the figure below shows this relation :

&igure "



Example :

The popula'on of a city in ())* is +,))) inhabitant, and the growth rate of the population in

this city is -..) % what is the predicted popula'on in ()+* .

Solution:

! "#

$%% &'&()*

+&'& , -()

(- Geometric increase method:

This method differs from the previous one in which the change in population is in a

direct proportion with the number of population. While the population varies from

year to another, the increase in population is not constant.

Ex: the popula'on in ())* .

the popula'on in ())0.

the popula'on in ()), .

the popula'on in ())1 .

! !%+& ,/

The relation between the time t and will be as follow :

P=-)))

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Example

: Solve the previous example by using the Geometric increase method :

Given:

Solution:

! !%+& ,/ +& ,=% &()

By comparing the two values of the population obtained from the first method (Arithmetic

method) and the second method (Geometric increase method) , it seems that the second

method gives more logical and accurate estimation of the population .

The figure below shows the two methods together:

&igure +



In any case , the value obtained from either the first method or the second method should

finally be compared with the saturation case of population in the city .

Example : calculate the saturation number of population in a city has an area of

*+.-))>?

To compute the saturation number of population just follow these steps:

Total area = *+.-)) >?

Area of residential area =0)% +@A,

' '>?

Area of buildings = *)% +)BC)A,

'>?

Assume that the common number of floors in the city for each building about . 7oors

Dtotal available residential area = ( E@FGH)AB)CI) +JI@FFA@@CH>G,

= = &>?

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C6Q3C6Q3C6Q3C6Q3::::

If the future population (, obtained from the Geometric increase < saturation case of

population (wbxcbdy)

In this case, the number of population that you should use in the design process is

# of Population

used in the design

process

population estimation

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