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Migration1 is a form of geographical mobility2 or spatial mobility2 between one geographical unit and another, generally involving a change of residence from the place of origin3 or place of departure3 to the place of destination4 or place of arrival4. Such migration is called permanent migration and should be distinguished from other forms of movement which do not involve a permanent change of residence (212-5). The concept of migration is applicable only in the case of relatively settled populations. In practice it is difficult to distinguish between migrants and visitors (310-5), but a distinction is sometimes attempted on the basis of the length of absence5 from the previous residence or the duration of stay6 at the new residence. Alternatively the distinction may be made on a juridical basis, depending upon the classification of a particular person as a resident or visitor by the government of the country having jurisdiction over the area concerned.
- 1. Migration n. — migrate v. — migrant n., one who migrates, also used as adj. — migratory adj., relating to migration.
With respect to a defined territory, external migration1 involves movement across its boundaries. Where the territory in question is a sovereign state, migration across its border is called international migration2. This term is sometimes used as a synonym for external migration, but the two are not necessarily equivalent. The terms immigration3 and emigration4 refer respectively to movement into or out of a particular territory. Migration within a given state, which consists of movement between different parts of that state, is called internal migration5.
- 1. A person who crosses a country in the course of migratory movement is considered by that country as a person in transit.
- 3. immigration n. — immigrate v. — immigrant n., one who immigrates; also used as an adj. The term in-migration is generally used instead of immigration in the case of migration which is not international; one who immigrates is an in-migrant.
- 4. emigration n. — emigrate v. — emigrant n., one who emigrates; also used as an adj. The term emigré is usually applied to a person who leaves his native country for political reasons. Where migration is not international, the terms out-migration and out-migrant are generally used instead of emigration and emigrant.
The term migratory movement1 is used for that section of total population movement which is due to migration (801-1). The total of arrivals2 of immigrants (802-3*) and departures3 of emigrants (802-4*) is called gross migration4 or the volume of migration4. Net migration5 is the difference between the total number of persons arriving and the total number leaving; it is also referred to as the balance of migration5. If the number entering exceeds the number leaving, there is net immigration6 in the reverse case there is net emigration7.
- 2. arrival n. — arrive v.
- 3. departure n. — depart v.
Migration statistics1 are compiled to reveal the volume of migration (801-1), the direction of migratory movement (803-1), and the characteristics of migrants (801-1*). The accuracy with which each of these kinds of fact is ascertained depends upon the method of compilation, as most migration statistics consist of approximations and estimates rather than precise measurements. Direct measurement of migration2 requires a system of recording movements as they occur. In the case of overseas migration they may be based on passenger records3 or passenger lists3 of ships and aircraft. Counts of persons crossing a political frontier yield only very crude data unless special steps are taken to distinguish migrants from travellers4, who do not change their place of residence. The number of visas5 or entry permits5 granted and the number of residence permits6 or labour permits7 issued may also be used as an indication of the migration of foreign nationals. Changes of legal residence (310-6*) noted for voting purposes, transfers of school registration and similar figures may be used as an index of internal migration (802-5). Each of these sources may reflect a variety of movements other than those defined as migration or may fail to include movements which should be counted as migration.
- 4. traveller n. — travel v. — travel n., the process of travelling,
- 5. In certain countries residents who wish to travel abroad are required to obtain exit permits or exit visas, records of which may serve as a source of information on migratory movements.
Where it is not possible to determine migration directly, the indirect measurement of migration1 involves estimates obtained by the residual2 method, in which the change in population between two dates is compared with the change due to natural growth and the difference between the two figures attributed to migration. The vital statistics technique3 consists of computing the difference between total population change and natural increase (701-7). In the survival ratio technique4 the death rates of the inter-censal period are applied to age (326-5) the census population and to give the expected population at the end of the period. A comparison between the observed and the expected population may be used to estimate the balance of migration by age. If it were possible to obtain data on either net or gross migration and on the mean population of the area concerned, migration rates5 showing the incidence of migration could be computed. In practice, however, it is extremely difficult to specify the population at risk and such rates are therefore rarely used.
The study of the mobility of a population is concerned not only with migration proper (in the sense of 810-1) but also with temporary movements. Among the latter, certain regular movements are particularly important. Commuting1 is the regular journey between the place of residence and the place of work, and seasonal migration2 takes place at certain periods of the year. Such seasonal migration is generally labour migration3, i.e., the migration of individuals coming to work for a certain season, e.g. the harvest.
- 1. commuting part. — commute v. — commuter adj. These terms are not generally used in England.
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