This idea of the linear river way being along the deepest part seems to
have been created in this thread. No such 'rule' exists, either in
practice, nor in Wiki tagging pages. The normal usage is to place the
way along the approximate centre line of the waterway, just as we do
with roads.
As to the direction, this usually can be determined by watching the
water flow, or simply by knowledge of the surrounding topography. There
are some problematic cases:
1. Contour canals have no flow. The direction or the way is arbitrary.
2. Canals that pass over summits flow away from the summit reach, so the
way must be split into two opposing directions at the point of the
feeder reservoir. Likewise at lowest reach between two summits.
3. River deltas often have channels that cross between two branches of
the same river. The direction of the way is arbitrary.
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