Charts give details of depth, land and sea marks, harbours and hazards.

The seas are much more difficult to navigate and chart than the land because obstacles remain hidden below the water. This is why having accurate charts, careful planning and keeping a constant lookout are very important to being safe at sea.

Knowing how to read charts is very important. You can't always rely on technology to find your way.

Charts colours

Charts have contours that show the shape of the sea bed. Different makes of chart use different colours. The Admiralty charts use colours in this way (depending on the scale of the chart):

Yellow Land
Green Areas that cover and uncover according to the tides
Blue Shallow water
White Deep water

Charted depths

Charts are covered with numbers. In the blue and white areas these are charted depths and they show the depth of the water in metres. All these depths are measured from the lowest tide likely to occur.


The compass on a chart is called a compass rose, this is used for navigation. It's divided into degrees, like a circle. So north is 0°, east is 90°, south is 180° and west is 270°.

The compass rose on a chart shows you the difference between magnetic north and true north for the area shown on the chart. The difference between magnetic and true north varies slightly all over the world. However, if you don't allow for this variation when you plot your course you could end up miles out of your way!

Buoys (cardinals, laterals)

  • Chart symbol for a port can

    Port can
  • Chart symbol for a starboard cone

    Starboard cone
  • Chart symbol for a west cardinal

    West cardinal
  • Chart symbol for an east cardinal

    East cardinal
  • Chart symbol for a south cardinal

    South cardinal
  • Chart symbol for a north cardinal

    North cardinal
  • Chart symbol for a north cardinal light buoy

    North cardinal

    light buoy

Symbols (wrecks, church spire)

  • Chart symbol for a wreck

  • Chart symbol for a church spire

    Church spire

See if you can find these symbols in the chart above.

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