International and internal migration are discussed separately in sections 4 and 5 below. The indicator is usually expressed as per thousand population. The net migration rate measures geographical mobility of population.
Net migration is a major force of demographic redistribution.
Within countries, migration both influences and is influenced by economic, social, environmental and political events. Increases of net migration linked to a loss of livelihood can be a symptom of unsustainability. It can also be a political phenomenon, as with asylum seekers and refugees. The significance of migration to national policy makers does not rest only in its size, but also in its composition. Such migrant characteristics as age, sex, fertility level, educational background, occupation, and skill levels have profound implications for development in both the sending and the receiving areas or countries.