The age and sex structure of a population may be best described by a
The age and sex distribution of a population is best represented by population pyramid
In countries with high birth rates as ours, it is broad based conical pyramid because of high birth rate and tapering of population with increase in age.
In developed countries with low birth rate, the pyramid swells in the middle and is narrow at the base and is not so conical at the top. (dumb bell shaped).

Utility of population pyramid 
Shape of population pyramid indicates fertility pattern

Broad base, Narrow top (upright triangle): High proportion of younger population (developing countries)
Bulge in Middle: High proportion of adults (developed countries)

Span (height) of population pyramid indicates life expectancy

Taller pyramid: Higher life expectancy (developed countries)
Shorter pyramid: Lower life expectancy (developing countries)

Symmetry of population pyramid indicates sex ratio

Symmetric pyramid: ideal sex ratio ( developed countries)
Asymmetric pyramid: unfavorable sex ratio <1000 (developing countries)
Life table
corelation coefficient
Population pyramid
Bar chart