Arithmetical
Increase Method
The method is generally
applicable to large and old cities. In this
method the average increase of population
per decade is calculated from the past records
and added to the present population to find
out population in the next decade. This
method gives a low value and is suitable
for well settled and established communities.
Incremental
Increase Method
In this method
the increment in arithmetical increase is
determined from the past decades and the
average of that increment is added to the
average increase. This method increases
the figures obtained by the arithmetical
increase method.
Geometrical
Increase Method
In this method
percentage increase is assumed to be the
rate of growth and the average of the percentage
increase is used to find out future increment
in population. This method gives much higher
value and is mostly applicable for growing
towns and cities having vast scope for expansion.
Decreasing
Rate of Growth
In this method
it is assumed that rate of percentage increase
decreases and the average decrease in the
rate of growth is calculated. Then the percentage
increase is modified by deducting the decrease
in rate of growth. This method is applicable
only in such cases where the rate of growth
of population shows a downward trend.
Graphical
Method
In this approach
there are two methods. In one, only the
city in question is considered and in the
second. other similar cities are also taken
into account.
- Graphical method based
on single city
-
In this method the population curve of the city (i.e. the population
vs past decades)is smoothly extended for
getting future value. This extension has
to be done carefully and it requires vast
experience and good judgement. The line
of best fit may be obtained by the method
of least squares.
-
Graphical
method based on cities with similar growth
pattern
In this
method the city in question is compared
with other cities which have already undergone
the same phases of development which the
city in question is likely to undergo
and based on this comparison, a graph
between population and decades is plotted
and extrapolated.
Logistic Method
The Shaped
logistic curve for any city gives complete
trend of growth of the city right from beginning
to saturation limit of population of the
city. This method is applicable for very
large cities with sufficient demographic
data.
Method of
Density
In the approach
the trend in rate of density increase of
population for each sector of a city, is
found out and population forecast is done
for each sector based on the above approach.
Addition of sector wise population gives
the population of the city.
Final Forecast
While the forecast
of the prospective population of a projected
area at any given time during the period
of design can be derived by any one of the
foregoing methods appropriate to each case,
the density and distribution of such population
within the several areas, zones or districts
will again have to be made with a discerning
judgement on the relative probabilities
of expansion within each zone or district,
according to its nature of development and
based on existing and contemplated town
planning regulations.
Wherever population
growth forecast or master plans prepared
by town planning or other appropriate authorities
are available, the decision regarding the
design population should take their figures
into account.
Worked out
examples for estimation of the future population
by some of the methods are given in Appendix
1.
