# Unit4 a Population Pyramids

```Population Pyramids
A Population Pyramid is two backto-back bar graphs. One side of the
graph shows the number of males
while the other side shows females
in a particular population in five-year
age groups. These age groups are
also called COHORTS.
Thus, a Population Pyramid is AGE
and SEX DISTRIBUTION within a
country.
A pyramid graphically displays long
term trends in the birth and death
rates, as well as shorter term
impacts such as baby-booms, wars
and epidemics.
Population Pyramids
“How it works”
Bar graphs are a
handy way to illustrate
numbers.
Graphing the number
of males and females
age groups according
to the 1961 Census,
the result would be the
two figures. The top
figure is % males in
population, while the
bottom figure is %
females.
Population Pyramids
“How it works”…2
Displaying these two
graphs together,
horizontally and as a
mirror image, a
Population Pyramid is
This figure shows the
1961 Population
In this period,
growing.
Interpretation of this pyramid.
It narrows toward the top. The death rate is
higher among older people than among
younger people.
There are not as many people in their 20s
as in their 30s. The people in their 20s in
1961 were born at the end of the
Depression and the start of WWII. This was
a time of economic hardship and
uncertainty. People were having fewer
children in this period.
In 1961, the pyramid had a wide base.
Adding the percentages for the three lowest
age cohorts, we learn that 35% of the
population was under 15. These are the
“baby boomers,” a large group of people
born between 1947 and 1966 when the
economy was growing and prospering.
Population
Pyramids
Population Pyramids
CONSTRUCTION
The X-axis illustrates males
and females. Males are
always shown on the left and
females on the right.
The Y-axis is age cohorts
Males and females can be
represented or measured by
the absolute number OR as a
percentage of the total
population.
Population Pyramids
Types of Pyramids
Expansive — A broad base indicating
a high proportion of children, a rapid
rate of population growth, and a low
proportion of older people.
Stable growth — A structure with
indentations that even out and reflect
slow growth over a period.
Stationary — A narrow base and
roughly equal numbers in each age
group, tapering off at the older ages.
This pyramid shows an unchanging
pattern of fertility and mortality.
Declining — A high proportion of
aged persons and declining
numbers.
Population
Pyramids
The triangular distribution is also be
called a pyramid or exponential
distribution.
In this example, the wide base
indicates a large number of children,
while the rapid narrowing shows that
many people die between each age
band.
The pyramid shows a population with
a high birth rate, a high death rate
and a short life expectancy. This
pattern is typical of less
economically developed countries.
Here, there may be little access and
incentive to use birth control, poor
environmental factors (e.g., lack of
health services.
Population Pyramids
Rapid Growth
The triangle shape
suggest rapid population
growth.
Population Pyramids
Slow Growth
The square-like structure
is slow growth. The lump
in the pyramid between
the ages of about 35 to 50
is the post-World War II
&quot;baby boom.&quot; As this
population ages and
climbs up the pyramid,
there will be a much
greater demand for
medical and other geriatric
services.
Population Pyramids
Negative Growth
The population is
shrinking due to a low
birth rate and a stable
death rate. Increased
emigration may also
be a contributor to a
declining population.
Population Pyramids
The following data are age cohorts for different countries
of the world. Build a Population Pyramid for each
country and describe the growth pattern.
Males
Females
0-19 20-39 40-59
60+
0-19
20-39
40-59
60+
13
15
14
7
12
15
14
9
Kenya
28
15
5
2
27
15
5
2
Germany
11
15
14
10
10
14
13
14
Pakistan
27
15
7
2
25
14
7
2
Poland
14
15
13
7
14
14
14
10
Population Pyramids
The figures illustrate four
different patterns or
characteristics of
population growth.
For each figure, describe
the pattern (e.g., high birth
rate, high death rate) and
the type of pyramid (e.g.,
Expansive, Stationary).
```