ENC Accuracy

Zones of Confidence (ZOC) define the accuracy of underwater feature depiction on ENCs in accordance with the IHO S-57 standard. CATZOC applies to both the horizontal coordinates of underwater objects and the depth measurement error.

The ZOC category is specified in ENC metadata and is used to assess the reliability of chart data during voyage planning and execution.

A single ENC cell may contain ZOCs of different categories.

Important

When planning and monitoring a route, take into account the ZOC category of the navigation areas. Categories A1/A2 provide the highest accuracy of bathymetric data.

To automatically account for CATZOC and automatically calculate XTD, enable CATZOC consideration in the route settings before laying the route.

Note

The data is provided in accordance with IHO Publication S-57 (International Hydrographic Organization Standard for Digital Hydrographic Data) and IHO Publication S-67. Mariners’ Guide to Accuracy of Depth Information in Electronic Navigational Charts (ENC).

ENC Underwater Feature Accuracy

ZOC Category	Position Accuracy	Depth Accuracy
A1	± 5 m + 5% of depth	± 0.5 m + 1% of depth Examples: Depth 10 m: ± 0.6 m Depth 30 m: ± 0.8 m Depth 100 m: ± 1.5 m Depth 1000 m: ± 10.5 m
A2	± 20 m	± 1.0 m + 2% of depth Examples: Depth 10 m: ± 1.2 m Depth 30 m: ± 1.6 m Depth 100 m: ± 3.0 m Depth 1000 m: ± 21.0 m
B	± 50 m	± 1.0 m + 2% of depth Examples: Depth 10 m: ± 1.2 m Depth 30 m: ± 1.6 m Depth 100 m: ± 3.0 m Depth 1000 m: ± 21.0 m
C	± 500 m	± 2.0 m + 5% of depth Examples: Depth 10 m: ± 2.5 m Depth 30 m: ± 3.5 m Depth 100 m: ± 7.0 m Depth 1000 m: ± 52.0 m
D	Greater than ZOC C	Greater than ZOC C
U	Unassessed — bathymetric data quality not evaluated	Errors not defined

Warning

Categories D and U indicate poor quality or unassessed bathymetric data. Extra caution and the use of additional navigational aids are required in such areas.