1. In the ’traditional’ past, salt and local precious stones and minerals were the major exportable goods of deserts.
2. United Nations: 1982. Demographic Yearbook32, 1980. New York, Table 1, p. 133.
3. Note the decrease in time for a one-billion increase: 85 years for the second billion, 35 for the third, and 15 for the fourth; note as well, a slow-down of increase in recent years, presumably related to the widespread acceptance of family planning in China, the Western World, and the Eastern bloc.
4. 7.9 per km2 for 1960 vs 22 for the entire globe, 86 for Europe. The densities for 1979 were 32 for the world and 98 for Europe. (United Nations: Statistical Yearbook 31,1979/80, Table 1, p. 2.
5. Cf. the classic studies of Isaiah Bowman, 1931. The Pioneer Fringe, New York, Amer. Geogr. Soc., Spec. Publ. 13; the companion volume of regional studies, Pioneer Settlement, ibid. 14, 1932, and Isaiah Bowman (ed.): 1937, Limits of Land Settlement, New York, Council of Foreign Relations.