A charted mark: symbol, position and attributes

A buoy at sea and its chart symbol are different things. The buoy has a body, dimensions, mooring and physical condition.

The chart presents an assigned position, symbol and attributes through graphical conventions. Good reading starts by separating these layers: where the aid is represented, what category it identifies and which characteristics are published.

A small silhouette is neither a scale drawing of the buoy nor a measurement of a nearby danger.

Under IHO convention, a buoy symbol includes a small basal position circle; the stylised body can be inclined. Its tip is not a hull coordinate.

Elements can be graphically displaced for chart clarity without changing the location indicated by the appropriate position reference. For isolated danger, aid and hazard need depiction without hiding the obstruction’s position.

Visual distance between symbol bodies therefore cannot be read as actual clearance.

Fields can be abridged or some may not appear at the selected scale. Shape, topmark, colour and light have their own conventions.

Missing information is not automatically filled with the most common characteristic. This lesson uses original fictional fragments; they contain no coordinates, harbour chart or passing recommendation.

Small buoy descriptions are often shorter and period may be omitted depending on scale and available space. This does not mean no period exists; it is simply not written in that format.

S-4 also specifies conditions for omitting the white abbreviation. These are chart-production conventions, particularly for paper charts: they do not guarantee that every plotter or app uses exactly the same symbol, colours or information window.

A floating aid has an assigned position but can move or go off station. Light changes, temporary marks and faults may appear in official notices before a new chart edition.

Edition, updating, scale and information date matter. If a photograph looks green when the record says red, possibilities include misidentification, colour perception, change or outdated information.

A discrepancy calls for evidence, rather than silently replacing the record.

For a first reading, organise the legend into five fields: rhythm, colour, period, elevation and range. Then connect it with the name and symbol.

This prevents the largest number dominating interpretation. Ten miles nominal range, for example, does not place the observer on a position line ten miles away; it is a published light property under reference conditions.

The observer’s position would need independent information. A light description and a position fix answer different questions.