Category of zone of confidence or the CATZOC are symbols displayed in modern ECDIS and used during the appraisal phase of the passage plan by the OOW to determine the depth’s accuracy level. CATZOC is based on position accuracy, depth accuracy, sea floor coverage area, and the survey method. The CATZOC also indicates the quality of the production process of the ENC and not simply the quality of hydrographic survey data.
It is important to understand that these values are approximate and indicate the lowest category of confidence that a survey or group of surveys can claim.Categorv A1 CATZOC
As we can see from the image above, the category A1 of the CATZOC is symbolized by a triangle with 6 stars inside. Category A1 is the most accurate that you can find displayed on ECDIS.
To summarize the value of CATZOC category A1:
Position Accuracy: +/- 5m
Depth accuracy: 0.50+ 19%d (this means that for a depth of 10m, the accuracy will be +/-0.6, and for a depth of 100m it will be +/- 1.5m)
Seafloor Coverage: The survey of the areas has been fully undertaken, and all the features of the depths have been detected.
Typical Survey Characteristics: The method used for the survey in the area where it is marked with category A1 is performed with DPGS and with sonar multibeam.
Category A2 CATZOC
This category is represented by a triangle with 5 stars inside it. The value of A2 CATZOC are the following:
Position Accuracy: +/- 20m
Depth accuracy: 1 2%d (this means that for a depth of 10m, the accuracy will be +/-1.2, and for a depth of 100m it will be +/-3.0m).
Seafloor Coverage: In this case, the bottom survey has been performed, and all the significant seafloor features have been detected.
Typical Survey Characteristics: The method used for the survey of this area has less accuracy than the ZoC A1, and usually, it is performed with a modern echo sounder and sonar.
Category B CATZOC
This category is represented by a triangle with 4 stars inside it. The value of B CATZOC are the following:
Position Accuracy: +/-50m
Depth accuracy: 1.00+ 29%d (this means that for a depth of 10m, the accuracy will be +/-1.2, and for a depth of 100m it will be +/-3.0m).
Seafloor Coverage: The seafloor in category B of CATZoC may not be achieved. There may not be any risk regarding hazards to the surface.
Typical Survey Characteristics: In this case, the survey could be performed using modern echo sounder instruments. The accuracy will be less than CATZOC A2.
Category C CATZOC
This category is represented by a triangle with 3 stars inside it.The value of C CATZOC are the following:
Position Accuracy: +/-500m
Depth accuracy: 2.00+ 5%d (this means that for a depth of 10m, the accuracy will be +/-25, and for a depth of 100m it will be +/-7.0m).
Seafloor Coverage: The complete survey of the area may not be achieved, and depth anomalies may be expected.
Typical Survey Characteristics: The accuracy of the survey adopted in category C of CATZOC is very low.
Category D CATZOC
An ellipse symbolizes category D of CATZOC with 2 stars inside. The value of D CATZOC are the following:
Position Accuracy: None, but worse than category C
Depth accuracy: Also, in this case, the depth accuracy of CATZOC D is not specified, but it is assumed to be worse than category.
Seafloor Coverage: The complete survey of the area is not performed. Large anomalies of different values may be found.
Typical Survey Characteristics: Poor quality of data and lack of information for the zone.
Category U CATZOC
Unassessed– The quality of bathymetric data is yet to be assessed.CATZOC quality rated as ‘U’ for “Unassessed“. ECDIS operators should investigate further. Many ENCs have simply not been assessed for CATZOC because the Hydrographic Office producing the ENC has not been able to complete the task, and Unassessed may not necessarily mean that the ENC is of poor accuracy. ENCS may still be used in these cases, but a documented risk assessment may be necessary.
