Lowrance for Mapping Options

By Lance Valentine

One of the great advantages of modern fishing electronics is the ability to see bottom contours on our units by using built in mapping data or by adding an external “map chip” into our units. In the past decade or so digital mapping has gotten better, more accurate and covers more lakes. But there still are issues with commercial mapping products.

The biggest issue with digital map chips is that a lot of lakes that we fish have never been surveyed with modern sonar technology. About 98 percent of the information on today’s map chips is simply digitized copies of old, inaccurate data from paper charts, some that were made with no intention of being used for accuracy or finding small pieces of structure. Originally maps were created by crews of several people out on the lake, usually in multiple boats. One crew would lower a line with a weight attached to the bottom and determine how deep the water was. This information was then relayed to the crew in the other boat which usually contained a cartographer and a surveyor. The surveyor would find a reference point on the shore, usually a large tree, and would determine position of the boat from that reference point. As the “depth” crew relayed depth information to the cartographer, he would work with the surveyor to determine their position on the lake outline. The data was then taken to cartographers to interpret and record the depth at the recorded locations onto an outline of the body of water. Obviously not a very accurate system but the best they had when most charts were made in the 1930 and 40’s. What ends up on your current digital map chip is just a digital copy of this inaccurate data for most lakes.

Luckily, today anglers have lots of choices that offer high quality, accurate digital charting options. When looking at your choices for digital mapping cards, look for a list of “enhanced” or “High Def” lakes. These lakes have usually been mapped using modern sonar/GPS technology and are extremely accurate in both location of structure and the depth of the structure. Also some smaller areas of the Great Lakes have also been remapped using the same technology. How does this modern technology work? Basically what happens is a survey crew (or your and other anglers) simply “log” or record what their sonar is capturing while on the water to a SD card in a sonar/GPS unit. The data captured includes “x,y,z” (latitude, longitude, depth) data for each sonar ping that is transmitted. The data is then uploaded into a computer which starts to connect pings with the same depth, creating a basic contour map of the bottom. Now a professional cartographer gets involves and examines the map for anomalies, differences in depth etc. and makes adjustments as necessary. Voila! A highly accurate contour map has been created for consumer use.

Now that we understand a little about how digital charts are made and why they can be so inaccurate in some cases, let’s discuss other options available on today’s digital charts. Most of the better map chips allow for custom depth shading which allows the user to assign different colors or shades to specified depths. This helps the angler more easily see and identify key depths to fish, how structures lay out, weed edges and other important fishing factors.

Another great option is the ability to designate a specific color or markings for shallow water. The angler can pick a specific depth and any water shallower than that depth will be shaded in a color or with an overlay to make it easy to identify shallow water for both prevention of running aground and to identify it for fishing. More advanced mapping chip options, like Lowrance C-Maps will show bottom hardness, vegetation density and other features. Some even allow for a pan and zoom feature, allowing the user to change the way they look at the contours and gives the angler the ability to look at structure from any angle, including from a fishes point of view!

The latest leap in mapping technology is the popularity of angler created maps using products like Lowrance C-Map Genesis. By using C-Map Genesis an angler can log sonar on their Lowrance unit, upload it to the C-Map Genesis server, and in a few hours C-Map Genesis will have a map ready to be used in the users unit showing any combination of depth contours (in 1, 3, 5 or 10’ increments), bottom hardness and vegetation density. Multiple maps can be loaded onto a single SD card and the user can choose which map to view while on the water, the ultimate in customization. Genesis maps also allow the user to adjust for rise and fall in water levels so the map depth is accurate with the true water depth.

Genesis maps also allow for custom depth shading, shallow water shading and viewing of the map on your computer. The ability to continuously add sonar logs to an existing map makes Genesis a great choice since the angler does not need to wait for map chip manufacturers to update their product with the latest, more accurate information. Below are three pictures comparing popular map options and how they show at the same area on the Detroit River. Map 1 is Lowrance Insight that comes standard with Elite and HDS units. Map 2 is a Navionics Platinum map chip ($225). Map 3 was created using Insight C-Map Genesis and also show bottom hardness (not available on option 1 or 2). As you can see from the pictures above, choosing the proper mapping product for your Lowrance is an important step to better fishing. Below is a comparison chart of some of our favorite mapping products for Lowrance units. Choose the best option for where you are fishing, but remember, sometimes to get all the information you want (bottom hardness, live mapping, navigation buoys etc.) you may need multiple map chips in your machine.

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