WHEN IS A MOVE A MIGRATION

This paper extends the traditional theory of urban location to derive a consistent model of inter- and intra-regional mobility. It demonstra tes that the two are behaviorally distinct. Workplace and residence re locations tend to be 'substitutes' in intra-regional mobility but are 'complements' in inter-regional mobility. PreVioUs empirical papers ha ve neglected the theoretical foundations of intra-regional mobility. I n consequence, they have made four types of analytical compromises: de fined 'migration' as any change in residence location, used job change s as proxies for workplace mobility, neglected commuting distances, an d used estimation techniques that do not reveal the underlying behavio r.