1. Agnew, J., 1997, Commemoration and criticism fifty years after the publication of Harris and Ullman's "The nature of cities." Urban Geography , Vol. 18, 4-6.
2. Austin, C. M., Honey, R., and Eagle, T. C., 1987, Cultural Geography . St. Paul, MN: West, 496, Fig. 12.9.
3. Ayeni, B., 1979, Concepts and Techniques in Urban Analysis . London, UK: Croom Helm, and New York, NY: St. Marti's Press, 13, Fig. 1.2.n
4. Bailly, A. S., 1978, 'Organisation Urbaine: ThLéories et Modèles [Urban Organization: Theories and Models], 2nd ed. Paris, France: Centrede Recherche 'Urbanisme, 111, Fig. 4.d
5. Bailly, A. S., 1992, Les Concepts de la Géographie Humaine [Concepts in Human Geogra phy], 2nd ed. Paris, France: Masson, 102, Fig. 1.