Australian Hydrographic Office

Important Information for Chart Users

• Chart Related Information
• GPS Receivers & Chart Datums
• Accuracy and Reliability of Charts

Important NotICE

This product includes all significant hydrographic information obtained by the Australian Hydrographic Office (AHO) at date of compilation. Significant information is updated fortnightly. All reasonable efforts have been made to ensure the accuracy and completeness of the information, including third party information, incorporated in this product. The AHO regards third parties from which it received information as reliable, however the AHO cannot verify all such information and errors may therefore exist. Where possible, indications regarding the reliability of information are noted or symbolised in the product. Users should familiarise themselves with the meaning of any notes or symbols. The AHO does not accept liability for errors in third party information, or the inappropriate use of this product.

Accuracy and Reliability of Charts and ENC's

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.