It is a systematic study of population. The term demography is composed of two Greek words, i.e. demos (people) and graphein (describe) viz. describing number of people in a specified time-period in a territory/location or simply, description of people. It studies changes in—(i) Population size, (ii) Patterns of births, (iii) Deaths, (iv) Migration, (v) Structure and composition of the population E.g. relative proportion of women, men and different age groups.

Mainly two varieties—(i) Formal demography (ii) Social demography.

The formal demography studies statistics or quantitative field and social demography focuses on the social, economic or political aspects of population.

These are census and surveys. These correct data in a systematic way on the people residing within a specified territory.