GPS Accuracy

[CNY Lee]

Anyone else who lives in the NY area notice that the maps on the Navionics card just aren't that accurate? Makes me mad because I would love to be able to go to a break and work it or troll a certain contour without haveing to spend close to an hour just to search it and lay way points on it then come back and troll later. I was just wondering if anyone else has had that problem in the North East, seems like everything is catered to the mid-West and Great Lake guys.

[jhebert]

For information about the accuracy of the Global Positioning System see

http://www.gps.gov/systems/gps/performance/accuracy/

I have never heard of any reason why one would think that the accuracy of the Global Positioning System favored receivers located in the Midwestern United States of America. The system is a global system and as far as I can tell and as far as I have read, the accuracy is the same anywhere on the planet. See the resource I linked above for more details.

For users in North America the accuracy of a position fix using the Global Positioning System can be increased by using the Federal Aviation Administration's wide area augmentation system and its space-based augmentation system, often referred to as WAAS. This provides enhanced precision for position fixes in North America. There are other space-based augmentation systems in other regions, such as EGNOS for Europe.

[oilguy]

I'm pretty sure he was referring to the Navionics map overlay not being accurate to true lake contour.

I've got the same problem with the Nav chip in Canada too. It's a rough idea of lake contour at best.

[Shellback]

I'm running a Garmin system, and many contours aren't accurate with their mapping either. Has cost me many a lure! I guess they all use some mapping originally developed by the govt.

[yarcraft91]

Unless Navionics has surveyed the lake, their map is probably based on published paper maps. Some paper maps are very inaccurate (I have a cabin on one of those lakes). If the Midwest states did a better job of preparing paper maps "back when", then the electronic maps will be better, too. Some of our paper lake maps were prepared in the 1930's from WPA survey teams drilling holes in the ice and taking soundings. In some cases, I swear those WPA guys sat in a warm cabin and drew the maps by imagination.

The electronic maps are created from paper maps by people who transfer the map data into a computer. That process has its errors as well. Sometimes, they just plain get the lat/lon data wrong. Navionics used to give you a free updated map chip if you discovered such an electronic map and sent them corrections. I sent corrections for a map that originally showed part of the lake in what is actually a corn field 2 miles from water.

[gsorenson]

Originally Posted by yarcraft91

Unless Navionics has surveyed the lake, their map is probably based on published paper maps. Some paper maps are very inaccurate (I have a cabin on one of those lakes). If the Midwest states did a better job of preparing paper maps "back when", then the electronic maps will be better, too. Some of our paper lake maps were prepared in the 1930's from WPA survey teams drilling holes in the ice and taking soundings. In some cases, I swear those WPA guys sat in a warm cabin and drew the maps by imagination.

The electronic maps are created from paper maps by people who transfer the map data into a computer. That process has its errors as well. Sometimes, they just plain get the lat/lon data wrong. Navionics used to give you a free updated map chip if you discovered such an electronic map and sent them corrections. I sent corrections for a map that originally showed part of the lake in what is actually a corn field 2 miles from water.

I had this happen as well, my Navionics map was about a quarter of a mile off for the lake we have our camper on. It would show me up in the woods yet when we were actually on the lake. I contacted Navionics, gave them the true GPS coordinates, the said they would send me a new map chip with the lake updated......that was several years ago, I never did get that updated mapping chip.

Lakemaster has since surveyed "my" lake and that map is very accurate, works great in my HDS units, but I can no longer get that chip so if something happens to it I'd have to look at Lowrances new maps I guess.

[yarcraft91]

Lakemaster surveyed the lake where I have a cabin, where, as I said earlier, the prior maps were very inaccurate. They made the high-res map available on the last version of their chip for Lowrance. Unfortunately, both my LMS-527 and LCX-27 were on the short list of units in which that Lakemaster chip would not work. Still waiting for Navionics to survey the lake...