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Schematic Mapping

Having no maps or charts, navigators must devise ways of constructing mental equivalents.

"Trigger Fish" is the name for one such way of conceiving of the geography of the navigator's world. It envisions five places. Four of them form a diamond to represent the head, tail, and dorsal and ventral fins of the trigger fish.

The head is always the eastern point and the tail the western one; but the dorsal and ventral fins can serve either as northern and southern or as southern and northern points respectively. The fifth place, at the center of the diamond, represents the fish's backbone. 

Any set of islands, real or imaginary, reefs, shoals, or living seamarks whose relative locations are suitable can be construed as a trigger fish. On a course between the dorsal and ventral fins, the head or tail can serve as reference island and the backbone marks midcourse.

Where it is possible to see two trigger fish arrangements in which the northern point of one is the southern point of another, navigators engage in what they call "turning the trigger fish." The southern trigger fish is mentally flipped northward, its dorsal fin serving as a hinge. As a result, the same place serves as dorsal fin for both, being the northern point of one and the southern point of the other.

It is also possible to have overlapping trigger fish, using the backbone of one as the dorsal or ventral fin of another. Navigators arrange their world into large trigger fish and into chains of contiguous or overlapping lesser ones. These exercises serve to organize the islands into schematic mental maps.