Navigation and the use of electronic, paper and raster charts

This article is about the use of electronic charts for safe navigation and how they compare to paper and raster charts. This is the Navionics perspective. You may learn more on this topic by reading the article by Theo Stocker from Yachting Monthly magazine.

Prudent navigation basics
The rules of prudent navigation say that one should never rely on a single source of information, but instead reference multiple chart systems operating simultaneously at different zoom levels, plus radar, echo sounder, and proper planning with things like Sailing Directions, etc. Skilled navigators know that all nautical charts have errors, regardless of whether they are electronic or paper, raster or vector, official or privately made. This is exactly why all navigation standards require that the captain use multiple sources of information, and not just the charts alone.

Importance of content
What matters for a chart is the content, not the media or the technology that is used. Just recently, the International Hydrographic Organization stated that less than 10% of the seas are charted as good as Mars and the Moon, and even that 10% contains lots of errors. For example, in one very popular passage for regattas between two islands in Sweden, one of the most accurately charted seas in the world, two rocks are not reported in the official charts (paper, raster and vector). They are reported in Navionics charts by way of crowdsourcing. See our Boating app and this video.

In fact, the Norwegian Hydrographic Office, in an official statement, estimates that as many as 35,000 rocks in Norway are uncharted, and that with conventional means it will take about 30 years to chart them all.

In most cases, electronic charts are no better than the paper charts they are digitized from, which are not designed for, and therefore not adequate for, blind navigation. Unfortunately, some have the wrong impression that an electronic chart, just because it is electronic, must be so perfect that one can rely on it blindly, even in narrow waters and fog, which is obviously dangerous.

Limitations of raster charts
Raster is a very old technology which, by the way, can be hazardous when applied to nautical charts. The reason is that paper charts were designed to be viewed in their full 60” presentation, which is the normal size of a paper chart; but when you see the same on an electronic device, you can only see a 4” window of the full-size chart, meaning you totally lose the context and are likely to miss very relevant features.

In terms of usability, raster charts can be compared to a digital version of a magazine done with a rudimental .pdf file; it simply does not work. Magazines and newspapers that are successful in their digital version are not mere .pdf files of the paper equivalent, but an entirely different animal, a so-called “liquefied” multimedia product that is easy and enjoyable to read because you do not have to squint your eyes, or constantly scroll and zoom to read a single line of text, and there is much more content. Raster charts were obsolete 30 years ago. Even though some people still like the looks of them, with proper time and space one could find gazillions of problems and inconsistencies.

Vector chart advantages
Properly made vector charts show more, not less, detail at certain zoom levels. You can see the difference using the Navionics Boating app with charts of the U.S.; take a look at any bay or sound, for example Chesapeake Bay, Long Island Sound or Nantucket Sound. Tap the layer selector on the lower left side of the screen to toggle between the S57 raster chart and the Navionics vector chart. You will see that at certain zoom levels the Government chart, which is a replica of the paper chart, is blank, whereas our chart is perfectly populated. We do not support raster per se, but you can make a comparison with any of the other apps on the market that do, and you will see the same blank bays at the same zoom levels.

 Official vector chart     Navionics chart     

Official vector chart (left) beside a Navionics chart (right)

Working together for better charts
At Navionics, we constantly work to improve our charts. However, that does not mean that our charts are error-free; all charts have errors! In addition to using all sorts of data ranging from high-resolution aerial photography, airborne laser scanners, and good ol’ sonars, we have developed very innovative crowdsourcing systems. In this way, all boaters can benefit from timely, updated, location-based chart content.

Community Edits has attracted contributions from hundreds of thousands of boaters using our mobile apps, resulting in the correction of countless deficiencies present in official Hydrographic Office charts. In addition to all kinds of marine-related content like lights, rocks, and seasonal buoys, Community Edits includes helpful points of interest like provisioning shops and seaside restaurants, all visible almost instantly by other Boating app users. These valuable inputs can also be downloaded to plotter cards via Freshest Data.

Another incredible crowdsourcing opportunity, SonarChart™ is an HD bathymetry map that enables any boater to contribute sonar logs, from a wide range of plotters and mobile devices, which continuously enhance the charts. With tens of thousands of changes made every day, the content of SonarCharts is very dynamic. Updates are available daily to Navionics customers via Freshest Data, an updating service available for one year, and can also be viewed for free with the Navionics WebApp.