Devices or systems, external to a vessel, intended to assist a navigator to determine position or safe course or to warn of dangers or obstructions to navigation. For onboard navigational aids, use NAUTICAL CHARTS or NAUTICAL INSTRUMENTS.

BUOYS, LIGHTHOUSES, NAVIGATIONAL MARKERS

WATER TRANSPORT AND SHIPPING

WATERWAY SIGNS AND SIGNALS

GLOBAL POSITIONING SYSTEMS

MARITIME SERVICES

MARITIME TRAFFIC

NAUTICAL CHARTS

NAVIGATION

http://metadata.un.org/thesaurus/1000184