# Some Key Words in Migration

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Migration:
Migration is a form of geographic mobility involving a change of usual residence between clearly defined geographical units. Migration is one of the most complete variables of the basic demographic statistics.
Migrant:
A migrant is a person who has changed his usual place of residence from a migration defining area to another during the migration interval.
Migration Interval:
Incidence of migration data completed/recorded with reference to specified period of time is called migration interval. Migration occurs continuously over time. So, it is counted with reference to a period. The period may be definite, that is,
-1 year
- 5 years
- 10 years and so on.

The period may be indefinite i.e. lifetime of the population area.
Departure:
The area from where move is made from migration is called the area of origin or departure. For the migrants, the area of origin may be either,
the area of residence at the beginning of the migration interval or
the area of residence from which the last move was made.
Arrival /Area of destination:
For migration, area on which a move terminated to migration is the area of destination.
A life time migrant is one whose current area of residence is different from his area of birth and the migration of such persons in a population commonly refers to lifetime migration. Lifetime migration occurs between birth and the time of the survey or census. So the area births of lifetime migrants differs at the census and survey data.
Migration Stream:
A migration stream is the total number of moves made during a  given migration interval and that have common area of origin and a common area of destination. Thus the no. of non-migrants is given by n-diagonal elements.

Population Density:
Population density is a basic measure of population distribution which is defined as the number of persons per area unit.
That is,
[Thanks to Jahid Turja]