Population, term refers to the total human inhabitants of a specified area, such as a city, country or Continent, at a given time. Population study as a discipline is known as demography. It is concerned with the size, composition, and distribution or populations; their patterns of change over time through births, deaths, and migration, and the determinants and the consequences of such changes. Population studies yield knowledge important for planning, particularly by governaments, in field such as health, education, housing, social security, employment, and environmental preservation. Such studies also provide information needed to formulate governament population policies, which seek to modify demographic, trends in order to achieve economic and social objectives.