William Blake, Auguries of Innocence . Common sense tells us that rivers, rails, coastlines, and abstractly equivalent lines across the geographic landscape serve not only as barriers to flows of people, goods, and services, but also as transmitters of these flows. The manner in which they serve as such has captured the imagination of geographers for many years. In a different environmental context, but an abstractly similar argument, Nystuen also sees the oyster as a boundary dweller in the fragile margin of Chesapeake Bay, anchored in the sandy shores of the land while deriving food from the fluctuating wavy water boundary that washes over the shore. Enduring ideas remain fertile because their simple, elegant character permit many interpretations.
Duality is a concept that is useful when looking at the whole of an entity.
A purely dual situation is one that exhibits perfect symmetry. In the Euclidean world they are not, of course, equally valid statements. Parallel Euclidean lines do not meet in a point. Mark Jefferson s provocative early twentieth century maps illustrate this idea. There are gaps between Euclidean dimensions.