This thread has shown prolonged interest and high enthusiasm. Posts have varied between those who emote well but have little knowledge or experience to experienced navigators, schooled in the traditional means of positioning, reluctant to let go of tried-and-proven methods.
There's absolutely no question that electronic charting is here to stay, and to it's advantages over paper charts
I believe it would be useful to review for a moment how electronic charts are made, and what they fairly represent.
RASTER charts are simply snapshots of paper charts
. They contain EXACTLY what the paper charts contain, both the good and the bad. They look exactly like the paper charts they derive from, because they ARE simply digital reproductions of those paper charts. In every aspect.
VECTOR charts are another matter altogether.
They are not all created equal, by any means. Perhaps the best ones are those made by governments, such as the NOAA ENC
charts. Here's what NOAA has to say about their vector chart production
is a vector database of chart features built to the IHO's S-57 standard. NOAA's Office of Coast Survey
, as the U.S. national hydrographic office, is exclusively responsible for production and authorization of NOAA ENC data in U.S. waters.
NOAA ENCs support all types of marine
navigation by providing the official Electronic Navigational Chart used in ECDIS and in electronic charting systems. NOAA ENCs support real-time navigation, as well as the collision
and grounding avoidance needs of the mariner, and accommodate a real-time tide and current
display capability that is essential for large vessel navigation. NOAA ENCs also provide fully integrated vector base maps for use in geographic information systems (GIS) that are used for coastal management or other purposes.
Building and Maintaining NOAA ENCs
In 1997, NOAA began a process of building a portfolio of ENCs that encompass the same areas covered by NOAA’s suite of approximately 1,000 paper and raster charts. The ideal and most accurate way to build ENCs is to recompile the paper chart from all of the original source material. Unfortunately, this process is impractical as it is far too labor intensive. Instead, NOAA ENCs have been compiled from source on those features that are deemed to be navigationally significant.
U.S. Army Corps of Engineers' federal project
limits have been captured from large-scale drawings. These precise coordinates of channel limits are being incorporated into the ENC. Likewise, high-accuracy positions are being used to chart U.S. Coast Guard aids to navigation. The paper chart has been the source for the remainder of items.
NOAA has utilized private contractors to build NOAA ENCs. Private companies are provided high-resolution source information such as U.S. Army Corps of Engineers channel limits, and aids to navigation established by the U.S. Coast Guard. Contractors are also provided with the latest version of the paper/raster chart. All NOAA ENCs that are built by private contractors are reviewed by NOAA cartographers before they are posted on the Internet
NOAA cartographers and private contractors (under NOAA supervision) apply updates to ENCs using high resolution original source material. As new source information arrives at NOAA headquarters, cartographers update NOAA ENCs using high resolution position and depth
(bold emphasis added)
MidlandOne is correct when he says that ENCs are built from a vector database. That is, when they are built by governments
. However, not all vector charts are built this way. Some, published by independent companies, utilize in whole or in part charts which have been digitized
from paper charts. This process is one which is akin to tracing an outline through paper, using an electronic pencil. Depending on who's doing the tracing, and how they feel that morning, the results can be quite accurate or they can be way off in some places.
Further, while vector charts sometimes include data to a greater depth
than do paper charts, they typically lack the information on shore-based features which can be very helpful to the mariner who knows how to use them.
What's true of both types of electronic charts -- raster and vector -- is that their depiction of the real world may contain significant errors, both of omission and of comission. Features may be omitted. Features may be misplaced. Spelling errors abound in vector charts, less so in government-produced raster charts.
Enter the GPS. When it's working well -- which is 99% of the time or more -- it will yield a reliable Lat Lon readout, with an accuracy measured in feet. The chartplotter
will take this reading and plot it on the chart.
Voila! There you are. Or, at least, there you think you are on the chart. Much of the time you may, indeed, be where shown on the chartplotter
. But, some of the time, you won't be. You won't be because the chart itself is in error. Raster or vector. Rarely, you won't be because the GPS is in error. Yes, it happens. A few years ago aircraft crossing the Atlantic were showing GPS positions about 300 miles north of their positions. Timing error from the GPS satellites. Software
glitches can occur. Murphy can intervene (don't ever forget, that little sucker is always aboard, lurking about and looking for ways to wreak havoc on your sensible and ordered world).
And, as noted several times above, lightning
and other electrical
difficulties can render your gps and/or your chartplotter useless -- for a few minutes or forever, depending.
What's all this mean?
To me, it means that the prudent mariner will use GPS, chartplotters, electronic charts, and ALL OTHER MEANS AVAILABLE to determine his position, and to navigate carefully. Including, inter alia: the Mark #1 eyeball, sometimes assisted by a good set of 7x50 binoculars. Paper charts. Fathometer. Radar
. Smells and sounds. Sixth sense (informed and experienced intuition).
When something doesn't seem right, it often isn't, despite what the chartplotter may say.
Don't be lured into a state of electronic hypnosis. Use your senses, all your navigational tools and, most of all, your brain.
Even in 2009 with all the marvelous electronic wonders available to us, navigation remains a fine art
, comprised of both science and informed judgment.