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In this system there are five types of mark which may be used in any combination.
Lateral marks indicate the port and starboard sides of a channel in the direction coming from seaward. In tidal waters the direction is normally defined as the direction of the rising tide or stream, while in non-tidal waters it is decided arbitrarily by the buoyage authorities. In Danish waters the direction from seaward is generally north to south and west to east, with variations to suit local geographical conditions. These variations will be shown on the chart.
Cardinal marks are used to indicate the direction in which a hazard or danger lies, and the marks are named according to the quadrant in which they lie in relation to the hazard or danger. They may be placed in a group of two, three or four round the area of the hazard, or individually to indicate the extremity of a hazard or danger, the limit of an area of shoal water or a bend in a channel.
Isolated Danger marks are placed on or above an isolated danger such as a rock or wreck with navigable water all round.
Special marks are used to indicate areas or features that do not primarily affect navigation, such as restricted or prohibited areas, firing ranges and pipe lines.
Safe water marks indicate mid-channel, routes or landfalls.
Details of all marks, symbols and abbreviations used an charts of the IALA system A are given in the British Hydrographic Office Publication Chart Number 5011.
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