An interesting subject area which, In Britain at least, involves both the effects of natural increase and the results of selective migration, is the concentration of elderly people in particular areas of the country. This is clearly of direct concern for social policy in general, and for area health and local authority planning in particular (Warnes, 1982; Warnes and Law, 1984). A second example, also from Britain, is the political and social implications of the selective immigration policy and its effect on both population growth and ethnic concentration and segregation (Peach, 1968; Anwar, 1979).