A Cruising Guide to Electronic Charts
The paper chart is dead! Long live digital cartography! But be careful.
Like it or not, printed nautical charts are on their way out, as more and more sailors turn exclusively to the electronic equivalents displayed on their plotters, PCs, and a growing mélange of smart phones and tablets. Now, please: Retorts about how one must always carry paper charts, at least for backup, are unnecessary. I’m just reporting what I see, and don’t see, on boats these days, and besides, I love paper charts. I believe that the charts most of us grew up with mark a zenith point in a long struggle by mariners to organize hard-earned data into an amazingly rich, even artful, graphic form. I can’t throw old paper charts away.
Electronic charts, on the other hand, have only been evolving for a few decades, not centuries, and their zenith may not even be on the horizon yet. But their core advantage—the ability to constantly and automatically plot your GPS position relative to charted and overlaid dangers—is extremely compelling. Consider, for example, that many cruisers in areas with poor official charting, like the San Blas islands, have taken to scanning guidebook sketch charts (which contain lat and long information at their corners) into charting programs such as SeaClear that, when connected to a GPS, can put a boat right on the chartlet and thus bypass the bother, and potential mistakes, of plotting guide waypoints manually.
Electronic charts can already be richer in data than printed charts—sometimes too rich—and eventually they’ll be even more intuitive, I trust, and maybe even better looking. But today they can be confusing in ways that lead to embarrassments or worse, and a good navigator, defined, in part, as a person with a slightly paranoid “What could be wrong here?” mindset, spends some time questioning the ones they use. Just where did this data come from? How current is it? Am I seeing all the critical information, and could I see it better? Are distances obvious? And what the heck is the underlying detail scale, anyway?
Getting a good feel for relative distances and data detail was relatively easy with paper charts, at least once you got used to the scale conventions of ocean, coastal, and harbor charts. And that knowledge, even if muddled a bit by such reprint books as ChartKits, which often mess with scales to make pages fit, can help you understand electronic charts better. That’s because nearly all the core navigation data you’ll see on the many current electronic-chart formats is sourced from the same place as the paper charts, often just traced off them. So while your display may let you zoom way in on a coastal complication, in all likelihood, you’ll see only the amount of detail a cartographer could fit on the largest-scale (showing the smallest area) paper chart for that area. That can vary a great deal between, say, a fairly infrequent 1:10,000 harbor chart and one designed at the common 1:40,000 coastal scale.
There are some interesting exceptions to that general concept, like the ultra-large scale C-Marina detail that Jeppesen C-Map folds into its electronic charts and the similarly high-resolution Corps of Engineers project data I sometimes detect in various manufacturers’ products. And sailors shouldn’t ignore the separate “fishing charts” now often bundled into digital cartography; it’s not official bathymetric data, but it’s often fresher than what is. For the most part, though, what you see on an electronic chart, aside from the sometimes useful extra data, like shoreside point-of-interest info, is simply a graphic reinterpretation of what’s drawn on the equivalent paper chart.