| Lines of constant tidal phase are called cotidal lines, which are analogous to contour lines of constant altitude on topographical maps. |
| A region surrounding an amphidromic point from which radiating cotidal lines progress through all hours of the tidal cycle. |
| High water rotates about the amphidromic point once every 12 hours in the direction of rising cotidal lines, and away from ebbing cotidal lines. |
| In the M2 plot above, each cotidal line differs by one hour from its neighbors, and the thicker lines show tides in phase with equilibrium at Greenwich. |
| The reason for these exceptions lies in the behaviour of the cotidal lines linking two amphidromic points. |
| South of Cape Hatteras the tidal forces are more complex, and cannot be predicted reliably based on the North Atlantic cotidal lines. |
