Electronic Charts
Very few updates to current U.S. coastal charts reflect current GPS positioning, other than ATONs (and then only when placed, as even they tend to move around). Most new chart editions are derived from mensurated satellite imagery.The digital charts (raster-scan and digitized vector varieties) used today by Garmin, etc. typically are sourced from the original paper charts. So the original errors plus new ones are propagated through these products. Many companies (e.g., MapTech, C-Map, etc) attempt to keep them updated to LNMs and issue annual upgrades. but if it isn't in an LNM, it isn't put into their product.Yes, GPS tells you where you are with amazing precision, but it's relative to a specific datum/geodetic model (i.e., WGS-84). Your chart may be relative to a different datum/geodetic model -- so cross-check!Dead-reckoning & coastal piloting isn't an exact science but it's pretty good if done by an expert. One important factor is that these techniques involve the full attention of the navigator to wind, current, depth, compass, speed log, landmarks, ATONs, birds, whatever. Also, it can be done with the simplest & most reliable instruments.Sticking your face into a GPS chartplotter is OK, but do it with the same overall situation awareness of the dead-reckoning navigator. It should be just one more tool, not THE tool.--RonD