Migration is defined broadly as a permanent or semipermanent change of residence. No restriction is placed upon the distance of the move or upon the volun- tary or involuntary nature of the act, and no distinction is made between external and internal migration. Thus, a move across the hall from one apartment to another is counted as just as much an act of migration as a move from Bombay, India, to Cedar Rapids, Iowa, though, of course, the initiation and consequences of such moves are vastly different. However, not all kinds of spatial mobility are included in this definition. Excluded, for example, are the continual movements of nomads and migratory workers, for whom there is no long-term residence, and temporary moves like those to the mountains for the summer.