More than depths

A nautical chart contains an enormous amount of information, if you can read it.

We’ve mentioned before that our tutoring consultant routinely posts maps on the wall of his cubicle, in a subtle attempt to increase the geographical awareness of his students.  Sometimes he asks for suggestions; recently one of the other tutors wanted one of Korea, since he was studying the language.  Our tutor wanted to be a little creative, so he borrowed a nautical chart of the Korea Strait from our navigator and posted that.  It actually got very little attention, the other tutor looking at it for a few minutes one day.

He found this a little annoying, because a nautical chart is such an efficient and effective way of presenting a lot of information.  There are the coastlines and depth of water, of course, the very basics.  But here are a couple of arrows showing the average strength of tidal current, next to a symbol for a lighted buoy that tells how it flashes at night.  Here is a lighthouse with a similar code along with its arc of visibility.  Over there is a traffic separation scheme, sort of like lanes on the highway, used when there are many ships traveling the same section of ocean in opposite directions.  Also marked are permanent fish traps and designated anchorages (also places where anchoring is prohibited), plus a sunken wreck (with the ominous tag “PA,” meaning “position approximate”). There are the paths of undersea cables and, here and there, indications of the character of the bottom (sand, shells, marl; there are two pages in the index to charts giving all the possible types).  Around the edges the latitude and longitude are marked, plus on grid lines; in convenient places there are compass roses big enough to show single degrees, together with the magnetic deviation (how far your magnetic compass points off true north).  Outlined are the areas covered by the next-smaller-area charts, so you know when to shift to them.  No road map shows anything like the same density and variety of information, and few land maps at all even approach it.

And all of it is, or was, of immediate importance and use to the mariner.  There are places to avoid and places to head for, and many clues to where your ship may actually be.  In the pre-GPS days the last would have been of supreme importance.  One would check off the lighthouses and buoys as one ran up the coast (and there was a detailed procedure to calculate how far away you should be able to see them).  Even the type of bottom could be a clue.  It was crude, of course, but you could cast a charged leadline (which means putting a sticky substance at the bottom of a weight at the end of a long rope, and lowering it until it hit the sea floor).  Not only would you measure the depth of water, you could compare the material you pulled up with what the chart said.  Even recently, you would check the bottom type to see whether your anchor would hold.

But none of the others at the tutoring center knows how to read a chart.  And, of course, most of the information would be useless to them if they could.  Our navigator is faced with sort of a reverse John Henry moment: an exercise of old technology or knowledge is not impressive to students, but completely incomprehensible.

Our tutor plans to stick to maps in the future.