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Passage Maker - - Electronics -

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.

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