The word demography comes from the Greek words demos (people) and spelling (act of writing), thus meaning "description of the population". It is the study of the size, composition and distribution of the population in the world, its variations and the causes that produce them.
In practice, demography is limited to the statistical study of the life of the man who lives in a certain community and which is affected by specific family, economic and social circumstances.
Demography is based on the analysis of factors such as the rates of birth, fertility, marriage, fertility, mortality, migration, or the growth rate in a given place and period.
In the study of the world population, certain elements of a physical nature (environment, relief, climate, hydrography, etc.), historical (economic oscillations through time and the set of beliefs, ideas, facts, catastrophes, institutional plans, etc.), and socioeconomic (public and private activity, sources of employment, technological processes, official policy, psychological factors, among others).
The population can be studied in two dimensions, where demography is classified as static, which deals with the structural knowledge of the population at a given moment; how many, who are and where the inhabitants of the considered population live, it defines characteristics such as age, sex, occupation, economic level and domicile.
The other demography is the dynamics, it deals with the evolution of these populations; that is, of changes over time in the structure of populations, and of the laws that determine that evolution. Characteristics are defined such as population growth, migratory balance, birth rate, fertility, mortality, etc.
Demographic research (surveys) and accumulated data (censuses, registries) provide us with information for a better understanding of the community, and are very useful because they allow rulers to plan, among other things, services, such as education., health and housing.
Demography is important for many reasons, ranging from productivity and savings to unemployment and inequality, and establishes differences in economic, human and social development in the regions of each nation and of the world.
