Who understands "maps chip upgrade"
You buy a depth finder you purchase a maps sd for it. I'm trying to figure out the upgrade, I understand improvements ramps,
Docks marinas above water development.
When I think of a underwater characteristic, such as a contour change channels
Foundations bridges an the like how do u upgrade something that was there when u bought the map to start with.
Or does upgrade just pertain to new lakes not offered when u purchased the maps program thanks.
On Dale I see garmin maps boat from time to time also a large deep vee hull with Map Surveyor wrapped boat
Thanks
Now Steve is someone that understands mapping data well
[B][I][U][/U][/I][/B]Those algorithms are just guesses as to what the ground is doing between two mapped points that are 100 yards apart. There could be a lot of up and downs or whatever in between the two map points. So the closer the map points are to each other the less error and the better the contour lines that are draw to make the map.
As George said the creek or DITCHES that were there a long time ago may be filled in with silt now or they could have changed course since the last big rain storm or since the lake was flooded. Some older digital maps were made by using aerial photographs of the area before the river valleys were flooded or the lakes were built.
Old aerial photos can be found using google earth historical data and come in handy if you can match the waypoints up on the aerial map which don't have gps coordinated on them and the map data you used in your fish finder.
When I was still in college our Physical Geology Class at USI and another environmental class that I took at Purdue University we have to take samples from the bottom of a lake and them had teams of surveyors on the banks taking readings of where our boat was located as we took each sample with a dredge. We lowered the dredge down to the bottom of the lake and they recorded our position in the lake. Then we mapped the lake bottom's soil type in class using our own eyes. We had to draw the contour lines using the map data, Depth reading as the different surveyed locations. We were studying a lake on the Purdue Campus out by the Airport and the Veterinary Medicine School.
At Indiana State University Evansville Campus as it was know back when it first started (now it's the University of Southern Indiana and has grown considerably) we had to draw a topo map by hand using certain know waypoints or data points with known elevations above sea level. It was not an easy job. The Professor did it easily as he had been doing this for a long time. But basically we were trying to make the contour lines go though areas of equal elevations. If you have a very steep drop off you can get by with using 30 or 50 ft contour intervals in the contour lines. But if the slop is gradual the contour lines will be too far apart. Say you are mapping Dale Hollow or the Grand Canyon area or a big mountain. That's where 5 ft contour lines are used in an area such as a flat. Such as a low land lake like KY lake or Lake Barkley. Most maps contour lines are drawn using engineering computer programs these days. Program's like AutoCAD are used or by now they probably have more specialized computer programs that can engineer the contour maps digitally.
Still the inaccuracy of the GPS data points can map the map data inaccurate. The waypoint you mark on your GPS may only be accurate to plus or minus 10 ft at times and that's a huge discrepancy if you are trying to drive your boat down a winding creek in a flat bay with stumps on each side of the ditch or creek channel. if you get off or out of the creek channel by a foot or two you can run into a stump under the water. That's why the companies that sell the maps usually put a DISCLAIMER on the map data saying to not use the map for NAVIGATION. :)
Now the extremely expensive surveying GPS can have accuracies as close at a few centimeters instead of meters. So they would be much more accurate and reliable. Still disturbances in the atmosphere can interfere with the timing of the timing signals which are used to determine your location on the earth. Any disturbance with the timing of the signals or any reflections or distortions can interfere with the accuracy of the devises. That's why they day that it's accurate to plus or minus 3 meters only [I][U][B]95% of the time[/B][/U][/I]. The other [B][I][U]5% of the time [/U][/I][/B]it could be much worse in accuracy. That's because the sun can change the amount of radiation that it sends our way or the earth's magnetic shield can vary in strength over time. At night vs the day when the sun is shinning directly on our side of the earth vs. when our side of the earth is shielded from direct sunlight.
[QUOTE=SteveM4A1;560713]Upgrades have to do with contours as well. When they map a lake, they don't cover every inch of it. They use algorithms to fill in the dead space. With each survey, the maps get more and more accurate. Just look at how accurate Sonarchart generally is compared to basic mapping. We live in an awesome time for marine electronics. Get yourself upgradeable chips from each and enjoy the wealth of information.[/QUOTE]
