Okay, I see what you mean
Since this portion of the discussion got started as a case in favor of greater sampling frequency for accurately marking turns, I pretty much kept that as my main point of contention. I see now that you really aren’t talking about not enough data, just imprecise data, so I have to agree with what you are saying here.
GPS Navigation
If you have a mapping GPS like a Garmin eTrex Legend or the GPS 60, they are great. If you have an entry level unit like the Garmin GEKO, its pretty much useless for what you want to do unless you have an accurate chart, map or aerial photo that you can plot your position on.
Also keep in mind that most mapping GPS’s are based on 10-20 year old USGS information, and can be lacking in the interesting little nooks and cranies contained in marshy areas.
I go out in simular locations, and I can relate to what your saying, I usually rely on my GPS, but have chart and or aerial photo for better reference.
ha…
…I’ve spent a small fortune on USGS maps (love to wallpaper with them!) and in saltmarsh areas, you might as well use them for TP. I’ve gotten lost plenty of times because these are based on 30 to 40 year old data, even with revisions. Even USGS will admit they should not be relied upon for navigation.
you can get recent revisions on some of these online at their regional websites (try your state abreviation & then geosurvey)
retracing your route
If that’s your concern, the Etrex at least, has a “Track Back” function that takes you back the way you came using trackpoints it previously laid down. Theoretically, you can get seriously lost in a marsh and it will return you the same way you came. You’ll test that out for us won’t you? 
At some more familiar place you could then use a goto to head to your own waypoints.
I agree
I have used GPS as an aid, trying to navigate though a maze of channels and dead ends, ascending the Clyde River in Northern Vermont (NFCT). Even breadcrumbs won’t help me if I am padding oneway upstream, as I usually do.
It is quite feasible to enter every maze decision point as a waypoint in your GPSR, but your ability to rely on this to make all the right turns is only as good as the map on which it is based. Even the most detailed topo maps of the area did not show us the fine detail of the river that would be required to avoid making many wrong turns.
Ultimately, it was local knowledge plus aerial photos that made getting through that sort of maze quite simple. The GPS is helpful, but only to the extent that the your map reflects every detail that you would need.
Garmin Etrex’s
Hi John,good to see your still here. In answer to your problem regarding GPS’s
I zig zagged from Blue Rock put-in up to the downed tree at the end of the island across from the putin and then paddled a straight line up and back. I got .4 of a mile differance. Don’t know if this makes the raspberries ripen any quicker but it seems to me that it is coming very close to what it is supposed to read wheather or not I make a turn or not.
I guess ,when the wheather breaks,we should go out and compare things like that just for the heck of it. Butches GPS doesn’t always read exactly the same as mine.He has a Legend and I have an Etrex.
Hopefully, I will be seeing you soon.
Gaylordsr
Some Experience
If you get mapping with your GPS you can do great in a salt marsh. I did it at Core Banks last year.