Hi Neil,

As you suggest, anyone using e-charts really owes it to themselves to gain a fuller understanding of exactly how they are created...

Here's a relevant excerpt that was published in OCEAN NAVIGATOR. I remember this one was first brought to my attention years ago by DougR, and I've linked to it numerous times since, probably most recently during the discussion of the grounding of ARCHANGEL off Camden last summer. Really is impressive, the body of work that a guy like Nigel Calder has created, his books are such wonderful resources...

http://www.oceannavigator.com/January-February-2003/How-accurate-are-our-charts/

"This is all a long-winded way of saying that the user of any chart should not be lulled into a false sense of security about its accuracy. Before GPS, there was always a degree of uncertainty about a boat's position. This led navigators to give a wide berth to hazards. In general, the techniques used to position hazards on a chart were more accurate than the nav tools available to the mariner.

Since GPS, this situation has been turned on its head. The equipment with which we navigate now has a positioning accuracy greater than that underlying the charts we use (including electronic charts, which are usually based on paper charts and old survey data).

Before you go shaving any corners, you need to have a thorough grasp of, and a healthy respect for, the limits of chart accuracy!"

best regards,

Jon