Christiansen, Sofus: Infield-outfield systems—characteristics and developments in different climatic environments. Geografisk Tidsskrift 77: 1–5, København, June 1, 1978. The infield-outfield system is defined, and its previous wide distribution noted. Its characteristics: efficiency, stability, and development are described. I-o farming is able to improve farmland by its ion-transfer mechanism. Finally its present survival in the North Atlantic region is explained by the system's rationality where altitude and climate restrict both expansion of infield and possibilities for ripening cereals.