Muller, P. O., Hames, E. M., & De Blij, H. J. (1997). Study guide, de Blij and Muller's 'Geography: Realms, regions and concepts' (8th ed.). Wiley.

Muller, Peter O., Elizabeth Muller Hames, and Harm J. De Blij. Study Guide, De Blij and Muller's 'Geography: Realms, Regions and Concepts'. 8th ed. New York ; Chichester: Wiley, 1997.

Muller, Peter O., et al. Study Guide, De Blij and Muller's 'Geography: Realms, Regions and Concepts'. 8th ed. Wiley, 1997.