migration: internal 3015

a permanent change in residence from one geo
graphical unit to another within a particular
country. For example, internal migration may
involve a change in residence from a rural area
to a city, from one city to another, or from one
region of a country to another. From the per
spective of the destination or receiving area, an
individual making such a move is an in
migrant, while that same individual is an out
migrant from the sending area. Because internal
migration has profound individual level and
collective repercussions, research on the topic
remains a popular endeavor for economists,
geographers, and demographers, despite the
absence of ideal data or definitional consensus.

THE IMPORTANCE OF INTERNAL
MIGRATION

The importance of migration derives primarily
from its position as one of the central demo
graphic processes that shape the size, distribu
tion, and composition of populations. Changes
in the size of a population can be thought of as
a function of two forces, natural increase (the
relative numbers of births and deaths) and net
migration (the relative number of in migrants
and out migrants). Whereas overall rates of
mortality and fertility tend to change fairly
slowly over time, the size of a population may
increase or decrease substantially over a short
period as a result of a sudden change in the
number of in migrants or out migrants. Thus,
internal migration tends to be the most volatile
component of population change for geographi
cal units within a country. Since internal migra
tion represents a redistribution of the existing
population of a country, internal migration
flows simultaneously affect the size of the send
ing and receiving populations, affecting compe
tition for food, housing, and other resources in
both locations. Economists have long viewed
internal migration as the primary mechanism
through which the equilibrium between the
distribution of economic opportunities and the
distribution of labor across areas of a country is
maintained.
Because migrants are rarely representative
of the populations in either the sending or
receiving areas, often differing from non
migrants in terms of average age, education,
race or ethnicity, and other sociodemographic
characteristics, patterns of migration have the
potential to dramatically alter the composition
of both sending and receiving areas. In fact,
large numbers of in migrants to an area may be
balanced by a similar number of out migrants
leaving the area, producing a relatively low level
of net migration, but a high level of total migra
tion (in migration out migration). While
such a pattern may have little effect on the size
of the population, it could, depending on the
relative characteristics of in and out migrants,
profoundly affect the composition of the popu
lation. Typically, high levels of internal migra
tion affect both the size and the composition of a
population, often with profound impacts for
social and economic conditions in both sending
and receiving areas.
The importance of migration extends well
beyond the effects on sending and receiving
populations; the effect on migrants themselves
is at least as profound. Conceptually, a migra
tion event not only involves a change in resi
dence, but also represents a change in social
environment and reorientation of the context
of daily activities. In many cases, internal migra
tion necessitates a search for new housing, com
petition for employment, and the loss of social
contacts developed in the place of origin. The
extent of these disruptions depends largely on
the type of move undertaken and the relative
social context of the place of origin and destina
tion; a move from a city to a neighboring city
may be less socially and economically disruptive
than a move from a rural area to an urban center.

DEFINING AND MEASURING
INTERNAL MIGRATION

Unlike fertility and mortality, migration has no
biological basis and cannot be measured
unequivocally. The definitional ambiguity of
the term is reflected in two aspects of the UN
guidelines. First, efforts to consistently define
internal migration are complicated by the
dubious permanence of many moves. The UN
guidelines suggest that a permanent relocation
is indicated by an absence from the place of
origin that lasts for at least one year. Following
this convention, internal migration is differen
tiated from daily commutes, vacations, and the