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How accurate are nautical charts? How much faith can be placed in them? Unfortunately, the answer is quite complex – far more complex than simply saying one chart is accurate whilst another is not.
All charts, whether paper or electronic, contain data which varies in quality due to the age and accuracy of individual surveys. In general, remote areas away from shipping routes tend to be less well surveyed, and less frequently, while areas of high commercial traffic are re-surveyed frequently to very high levels of accuracy, particularly where under-keel clearances are small. It is quite accurate to consider a chart as a jigsaw of individual surveys pieced together to form a single image. Having the necessary skills to determine how much confidence should be placed in the surveys which combine to form a chart should be essential for any mariner venturing into unfamiliar waters.
The attached guide on Accuracy and Reliability of Charts contains both explanations and examples intended to assist mariners in vessels of all sizes to determine how much confidence they should place in charts.
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