Many countries throughout the world have agreed to use a uniform system of coding navigational marks.
There are five types of marks which may be used in various combinations.
Lateral marks indicate the port and starboard boundaries of a route to be followed e.g. channel.
Lateral marks differ between buoyage system A and buoyage system B.
Cardinal marks indicate where the mariner may find navigable water.
These marks are used in conjunction with a compass.
Isolated danger marks indicate to a limited extent isolated dangers having navigable water around them.
Safe water marks indicate the location of navigable water surrounding their position, e.g. middle channel marks.
And, special marks not intended to assist navigation but which indicate special features e.g.spoil grounds or prohibited anchorages.