Seamarks/Seamark Tag Values

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Seamark Tagging
General Information
INT-1 Cross Reference

Tags for Nautical Chart Features

The following is a list of valid keys and values of tags used for nautical charts. Only tags with these keys will be interpreted by the various nautical chart renderers.

Seamark Objects

The tags described in these pages may be placed on any node, way (open or closed) or multi-polygon. The direction of ways making up a multi-polygon, either inners or outers, is not important. Only relations with at least one member with role outer and whose outer members form at least one closed area can be processed.


All tag keys and values are based on elements defined in the object and attribute catalogues of IHO S-100. The six-letter mnemonics used in that standard have been replaced by words or underscore separated English phrases for human readability. The format of tags is as follows:

<object> is the object key
<attribute> is the attribute key
<value> is the attribute value

Any given node or way can be tagged with more than one S-100 object - e.g. a buoy with a light and topmark would be tagged with three objects and their attributes. These objects are structured as a master-slave relationship with one master and zero or more slaves. The master object is indicated with a tag in the form:


with a value corresponding to a valid object key. This tag must be used (once and only once) on a node or way to be rendered in nautical charts. If it is absent, the renderer will ignore all other seamark tags on that node or way.

Note that in the case of LIGHTS, there are two possible symbols (light_major & light_minor).

Attributes with more than one value should specify those values by a semi-colon separated list.

Attributes that are common to all objects on a node or way should be specified in the form:


e.g. There is usually only one name associated with all objects on a node or way. This name should be specified by the tag:

seamark:name=<text string>


An example of this tagging scheme is illustrated here. This is of a buoy with topmark and light:


Object Index

A complete index to S-100 objects and their OSM tag names: Seamark Objects

Attribute Index

A complete index to S-100 attributes and their OSM tag names: Seamark Attributes


INT-1 Cross Reference