how many boaters even knew about Source Diagrams and how many will notice ZOC diagrams when paper charts are going out of use and the quilted raster charts seen on many apps, charting programs, and MFDs often don’t display the off-thewater information blocks and diagrams very well?
Here’s the good news: NOAA is encoding ZOC information into its ENC vector charts and have already completed Texas to Virginia and are working their way up the rest of the East Coast. That doesn’t mean we can see it yet in plotters that display ENCs or in the C-Map, Navionics, Garmin, etc. vector charts based on NOAA data, but all that is quite possible.
Recall that what we see on vector charts is a combination of the underlying data and the software that processes the data for display. And, by golly, NOAA is apparently making it possible for vector chart makers to display ZOC info in useful ways. Lead Nautical Cartographer Sean Legeer told me the following: “The ZOC information is encoded as a metadata object called M_QUAL and is a simple polygon. So it should be able to be shaded any way an ECS manufacturer would like. The attribute CATZOC in this object can be used to estimate the accuracy or uncertainty. We also provide the date of surveys.”
In fact, longtime C-Map manager Ken Cirillo had already told me that they are considering an optional ZOC layer that will shade your actual electronic chart (not a diagram) with the confidence zones and enable pop-ups of the details. So that’s possible. And, heck, it seems possible that a boat wandering out of the A1 Humboldt channel and into Zone D could get a screen warning about how much the chart’s accuracy is changing.
And, by the way, Humboldt Bay is not exceptional given what’s seen on all four of the ZOC charts (see photo at top) and how ZOC accuracy estimates seem to relate to the existing Source Diagrams.
In addition to serving as Senior Electronics Editor, Ben Ellison writes and maintains Panbo, a blog dedicated to the reviewing and reporting on the latest and greatest in marine electronics. Visit for more.