# Demography-3-2: Population Pyramid

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Population Pyramid:
A population Pyramid shows the total picture of a population by age & sex. It is a useful way to illustrate the age structure of population.
Forms of Pyramid:
Pyramids are of different shapes. The shapes are determined by 3 factors.
1. Fertility
2. Mortality
3. Migration
Therefore each rectangle representing an age or a group of ages has length that depends on
a. The total population at birth of the corresponding cohort or group of cohorts
b. The amount of reduction by mortality &
c. The amount of migration
The Construction of a Pyramid:
In a pyramid the absolute number in each group can be represented by a rectangle. Ages are located on the vertical axis & the total of each of the different ages (or age groups) are shown on the horizontal axis.
The rectangles are placed on top of each other, the youngest age group at the bottom & the oldest on top.
The rectangles for males are shown on the left side of the diagram & those for females on the right side. The open-ended age group can be represented only approximately.
As for example, If the open-ended age group is 75+ (75 years and above) we can treat this as 75-80 age group & draw the rectangles in this age group.
Pyramid from following table:

The population for males in 0-4 age group is

Similar calculation can be carried out for the other age groups (both for males & females).
The Pyramid: