A chart is an aid to navigation but not necessarily a precision instrument and sometimes the representation of reality can in some aspects be incorrect.

Depth representation may be incomplete due to a lack of modern surveys. Coastlines and islands may have errors of position due to older production methods whereas today aerial photography and GPS is used. Positions of permanent navigational aids and lighthouses may be incorrect due to not yet being positioned by modern methods. Wharves, jetties, bridges etc. may have been altered without the chart producer being informed.

In addition there are always the inherent cartographic errors produced by representing curved surfaces on flat charts. Also the scale of a chart make it impossible to reproduce land contours in minute detail and the cartographer is forced to generalise the picture so that important features are retained and perhaps even accentuated.

Another unavoidable limitation is the accuracy of manual drafting which is normally 0,2mm and at the end of the production chain results in a mean radial error of 0,5mm.

These limitations on reliability are relevant for all charts on the market whether paper or digital.

In order to avoid serious consequences due to the inaccuracies named above the navigator should take the following precautions:

• Keep to the fairways unless it is absolutely necessary to do otherwise. Fairways are better surveyed than surrounding areas.
• Navigate with a wide margin. Do not cut corners near promontories and shoals. Keep well clear of depth contours that constitute a danger to the vessel. Depth contours are warning signals!
• Leading lines on charts are verified and therefore reliable. However when constructing ones own leading lines there is no guarantee of clearing shoals in close proximity to the line.
• Charts of the largest available scale should always be used. In those areas represented by a larger scale chart or plan the ordinary chart contains only limited information.
• Important information for safe navigation can be given in the publications, Swedish Pilot, Maritime traffic regulations and Notices to mariners.

Much information on charts and in publications originates with other authorities and organisations who are in turn responsible for the correctness of this information.

If you discover an error on a chart or other product from the Swedish Maritime Administration, you may report the error by e-mail (click “Contact us”), or if you prefer, call, fax or write us (details below).

Mailing address:
The Swedish Maritime Administration
Chart Department
Ufs/Baltico
601 78 Norrköping, Sweden

Phone: +46 (0) 11-19 10 45, (0) 20-33 11 66
Fax: +46 (0) 11-23 89 45
E-mail: ntm.baltico@sjofartsverket.se