For a semi-diurnal tide the amphidromic point can be thought of roughly like the center of a clock face, with the hour hand pointing in the direction of the high water cotidal line, which is directly opposite the low water cotidal line.
12.
The amphidromic point is at once cotidal with high and low waters, which is satisfied by " zero " tidal motion . ( The rare exception occurs when the tide encircles an island, as it does around New Zealand, Iceland and Madagascar . ) Tidal motion generally lessens moving away from continental coasts, so that crossing the cotidal lines are contours of constant " amplitude " ( half the distance between high and low water ) which decrease to zero at the amphidromic point.
13.
The amphidromic point is at once cotidal with high and low waters, which is satisfied by " zero " tidal motion . ( The rare exception occurs when the tide encircles an island, as it does around New Zealand, Iceland and Madagascar . ) Tidal motion generally lessens moving away from continental coasts, so that crossing the cotidal lines are contours of constant " amplitude " ( half the distance between high and low water ) which decrease to zero at the amphidromic point.
