How to read a nautical chart

The nautical chart contains a lot of information beyond depth conditions – for example, scale, datum, warnings, etc.

The booklet "Symbols and abbreviations in Norwegian nautical charts" gives you important information and a good overview of all chart symbols and abbreviations used in Norwegian and international nautical charts.

Scale

When sailing in narrow waters, you should use nautical charts on the largest scale possible, as these provide the best and most detailed information. Smaller-scale maps are greatly simplified in inland waters.

The official Norwegian nautical chart portfolio published by the Norwegian Mapping Authority contains nautical chart series for main series charts, harbour charts, coastal charts and over-sea-navigation charts. The different chart series have scales that are adapted to different user needs.

ZOC Diagram

A ZOC- (Zones of Confidence) chart in a main series chart (scale 1:50,000) is a small and generalized map image at a scale of 1:500,000 that is placed in a suitable place in the paper map.

The most important function of the ZOC -chart is to highlight areas where the depthdata is of significantly poorer quality, i.e. where there is a greater risk to navigate.

Read more about data quality in Norwegian nautical charts (CATZOC)

Warnings

Outside the chart frame, information has been entered with warnings for, among other things:

• Speed restrictions
• Cables (overhead cables and underwater cables)
• Tide
• Vertical clearance under bridges and overhead cables

Plans and vignettes

In some nautical charts, you will be able to find small charts in the following frames: Vignettes and plans.

The vignette shows an area in the chart where the chart image goes beyond the boundaries of the chart itself, for example a long fjord for which it is not possible to expand the chart frame. The vignette has the same scale as the chart itself. "Continued on Plan" is written in red along the chart frame where the voyage continues into a vignette.

A plan is a section of the chart that is displayed in a separate chart frame. The plan show an important part of the nautical chart on a larger and better scale, such as important harbours and narrow passages. Areas where there is a plan are marked with a red border and the text "Plan" in red in the chart itself.

The map frame around vignettes and plans is similar.

Datum and chart projection

All Norwegian nautical charts are made in the datum WGS84 (degree grid). Which means that positions from GPS-based systems can be used directly in the nautical chart.

Chart projection is indicated in the title field at the top left of the map.

QR code

The nautical chart has a QR code that makes it possible, using a smartphone or tablet, to access all corrections related to the nautical chart. You also get access to all the information about the nautical chart and validity.