Category of zone of confidence is an ENC attribute rating the source survey for each area as A1, A2, B, C or D, with U for unassessed. A1 means a full seabed search with tight position and depth accuracy and all significant features detected; D means poor or sparse data. Paper charts show the same idea as a zone of confidence diagram. Mariners and pilots use it to decide how much margin to keep under the keel.
Approach is CATZOC C off a sparse lead-line survey, that's why the pilots want 2 metres of margin.
Also heard as
- zone of confidence
- ZOC
Related terms
ENC
Electronic navigational chart: an official vector chart database used in ECDIS, built from objects with attributes.
S-57
The international data transfer standard behind most electronic navigational charts, built on objects and attributes.
Coverage
The portion of the seabed actually measured or imaged by a survey, expressed as a percentage of the area.
Nautical chart
A map of waters and coasts made for mariners, showing depths, hazards, aids to navigation and landmarks.