North-Northwest

North-northwest is a bearing of 337.5 degrees, midway between north and northwest. As with the other secondary points, its interest is practical rather than symbolic. It is worth noting that a compass needle does not point to true north but to magnetic north, and the difference between the two, called variation by mariners and declination by surveyors, can be several degrees or more and changes both with location and over time as the Earth's magnetic field drifts; charts are annotated with it, and it must be applied to convert a compass bearing into a true one. Chinese use of the magnetic needle for orientation, initially in geomancy rather than navigation, is attested considerably earlier than in Europe, and the Chinese also recorded the fact that the needle does not point true north, an observation made there before it was made in the west.

North-northwest is one of the thirty-two points of the traditional mariner's compass rose, bisecting north and northwest at 337.5 degrees, part of a subdivision system that grew out of medieval Mediterranean navigation, where portolan charts from at least the thirteenth century onward show compass roses marked with this finer thirty-two-point graduation alongside, and eventually replacing, the coarser eight- or sixteen-point wind roses of classical antiquity. Sailors were traditionally drilled in boxing the compass, reciting all thirty-two points in order from memory, a skill required of apprentice seamen in the age of sail for reading a magnetic compass card quickly and precisely enough to hold a course, a practical navigational discipline rather than a symbolic or cosmological one.

North-northwest, at 337.5 degrees, sits on the boundary between two mountains of the Chinese geomantic compass: Hai, the branch of the pig, and Ren, a heavenly stem occupying the arc immediately west of due north.

The luopan divides the horizon into twenty-four mountains of fifteen degrees each, built from the twelve earthly branches, eight heavenly stems and the four corner trigrams. The European rose divides it into sixteen or thirty-two points of 22.5 or 11.25 degrees. The two schemes agree on the four cardinals and the four intercardinals and on nothing else, and each of the eight secondary points of the sixteen-point rose falls precisely on a boundary between mountains rather than at the middle of one.

Hai is the last of the twelve branches and Ren stands next to Zi, the branch of due north, so this particular boundary is close to the seam where the cycle of the branches closes and begins again. In the reckoning of hours, Hai is the double hour from nine at night to eleven, immediately before the hour of the rat that contains midnight.

For a navigator the 22.5 degree point is a bearing like any other. For a practitioner reading a luopan it is a line between two readings, and the compass schools treat a building or a grave aligned exactly along it as sitting on nothing. The same arc of sky, divided by two arithmetics, produces a usable direction in one system and a gap in the other.