Map Accuracy

[IcePro]

This is not a question on which map chip to buy (Lake Master or Navionics) since I own both.

The question I have is which map is more accurate or detailed for structure and way points? When I compare a lake that is on a high contour map for both (i.e. Mille Lacs or Lake Minnetonka) you notice a difference in the mapping detail.

For a comparison look at both maps for Browns Bay on Lake Minnetonka you will notice a significant difference on the map detail.

Also when you compare way points on a comparable spot on both maps there will be a variance in way points as well.

To even complicate things further I have compared the newer Lake Master map with an old Lake Master map (2001) for Mille Lacs and there is a difference between them as well. However the older Lake Master map is identical to the newer Navionics map.

I have the Nav Planner from Navionics so I can look at their maps on my computer and I also have the Lake Master Contour Pro PC Mapping Software thus allowing me to compare both maps side by side on my computer.

It appears Navionics maps have greater detail than the newer Lake Master map. Again how do you know which one is more accurate? I guess I will need to put in both chips into my GPS on the lake and research.

Has anyone else compared both maps side by side?

[Warren]

I have been to Doc Samson's Lowrance School & Mapping Seminar.

I believe that when ~50 or so years ago the technology was improved. As an Example the GPS with WAAS improved.

They will troll a Grid, so it's how far apart or how close that the interpolation has to be computed. The closer the Grid the less error in the interpolation that could be in error.

A program to make your own maps is DRDepth , but I bet the Boats Transducer is not the same that Lake Mapper of thos eHigh Density MAps that are comming in now, from Lakemaster and Navionic's.

Thats why we need our sonar to confirm contors errors :}

It's like a fine wine getting better

[irishwalleye]

My personal favorite is finding structure that doesnt exist on the mapping chip. This happens to me constantly on Clearwater and I talk to LakeMaster about this every chance I get.

[so haaad]

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My personal favorite is finding structure that doesnt exist on the mapping chip. This happens to me constantly on Clearwater and I talk to LakeMaster about this every chance I get.

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Careful what you wish for. I actually like that lake maps don't always show everything there is.

[fishinJohn]

I need to start diving... or make friends with those who do!

[Hotspotter]

IcePro:

I work in the GIS/GPS field, and may be able to answer some questions.

Map chip accuracy is different than waypoint/GPS accuracy. Think of the points locked into space, but independent of the map it's being displayed upon. Once you lock-in your GPS location as a waypoint, it will appear in the same place everytime. Your background maps are the ones that are differing.

Warren hit it right on the head with the interpolation. The name of the game is that the quality of the mapping is directly dependent upon the quality of the survey done. More points is more information, but not every square inch of the lake-bottom can be sampled. Instead, complex statistical interpolations are run to get avg. depths between points sampled.

As always, the devil's in the details, with some surveys only making many, detailed, multiple passes in areas where there is detailed structure. Areas with less structure or more basic are sampled less intensively. This is the primary reason you'll have areas on map chips that are missed.

As far as fishing is concerned, these smaller, out-of-the-way spots amidst a sea of featureless bottom can be phenomenal fishing spots. I think this is where what Warren's talking about comes into play most, is achieving incredible detail for smaller areas with your boat's sonar/GPS.

Warren, shoot me an email if you get a chance. Address below.

Thanks!

Joel

[irishwalleye]

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Map chip accuracy is different than waypoint/GPS accuracy. Think of the points locked into space, but independent of the map it's being displayed upon. Once you lock-in your GPS location as a waypoint, it will appear in the same place everytime. Your background maps are the ones that are differing.

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I hate to say it but this makes it sound like there is no point in purchasing the chips if they are unable to work alongside the unit.

[irishwalleye]

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Careful what you wish for. I actually like that lake maps don't always show everything there is.

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I wouldn't even mention it but there are two places on Clearwater in particular that are so large that is HILARIOUS that they are not on the map. And I'm not talking about a 2 - 3 foot difference.

[IcePro]

I did a search for Dr Depth and came across their HSOforum.

Very informational on how you can create your own contour maps with a simple gps and computer.

If you search their site they will show you examples on how the map program works.

The cost of the program is only $115.00

Now if Lowrance, Humming Bird or Garmin would build this into their units it would be the route to go.

The down side is that you have to be able to plug your GPS into your computer. My Lowrance Expedition C does not allow this, glad I still have my Garmin hand held.

Has anyone actual used the Dr Depth Program?

[mhjohns]

I have two lakes that we fish on a regular basis. With the lakemaster chip, one shows a road going right through the lake (a raod that doesn't even exist) and the other is off by about 20 feet. Same thing there I noticed it when I saw the road on top of that lake also.

Thank goodness I don't use the chip to navigate in near zero visibility.

[fishinalot]

So Haaad is right. I would not like any of these maps too accurate!

I have my own spots that took me waaaaay too many years to gather up!!