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Are your fishing maps medieval? (Spoiler alert: Many are)


According to legend, when the makers of medieval maps didn’t know what lay beyond the horizon, they inked their parchments “here there be dragons” to prevent unwary sailors from disappearing into uncharted waters.

If only your fishing maps came with similar warnings.

Okay, so your fishing maps might not be medieval, but they’re probably as thorough as you think they are. And while there might not be dragons in the uncharted waters on your maps, there might be fish, and big ones! But how would you know?

Many fishing maps might as well be medieval, with as much guesswork lies behind many of their contour lines and how much uncharted, fish-holding structure likely lies between those lines.

‘Enormous gaps’ in legacy map data
The source data for many fishing maps ­might shock anglers who rely on maps to find potential fishing spots.

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DID THESE GUYS MAKE YOUR FISHING MAP? In this photo from the late 1930s to early ’40s, a lake survey worker makes a depth sounding with a lead line. According to one published report, the charts available in the “vast majority of electronic cartography” are based on historical data gathered similarly. (Photo source: National Oceanic and Atmospheric Administration/Department of Commerce)

According to one published report, the charts available in the “vast majority of electronic cartography” are based on historical data from the National Oceanic and Atmospheric Administration (NOAA) and/or from governmental agencies like state departments of natural resources (DNRs). For many lakes not sonar-charted by survey boat, very little data exist, other than the information in those old surveys. That historical data – which can be 50 or more years old (note the photos at right) – is often just integrated and repackaged. That can mean a new map is actually pretty old.

Many depths displayed on historical lake charts were determined by a man in a boat dropping a lead weight to the bottom on a rope. That process is called taking a “sounding.” Contrary to popular belief, the term “sounding” refers not to noise, but rather derives from the Old English word “sund,” which meant, in various contexts, “swimming,” “water” or “sea.” According to the report mentioned earlier, some historical depth charts might be based on only “four or five soundings for the entire acreage” of a lake, so map-selling companies contract survey crews “to plug the enormous gaps that exist in the DNR data.”

Unfortunately for anglers, the number of lakes that have actually been surveyed is likely but a drop in the bucket of lakes that we actually fish. More than likely, the lakes that you fish have not been surveyed by a commercial crew – and never will be.

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Lead lines similar to these have been used for centuries to measure and chart water depths. (Photo source:

This means the map of your lake – whether it’s on paper or a map chip – could be merely a glitzed up version of an old DNR map plagued with “enormous gaps” in the data, using the wording in that published report mentioned earlier. It’s in those gaps that fish are often hiding.

Insight Genesis will find those fish for you to catch.

Insight Genesis is a cloud-based service that empowers anglers to locate fish-holding structure on detail-rich, custom maps of the lakes they fish– no matter how big or small. With Insight Genesis, you can make your own fishing map and confidently mark it “Here there be FISH.”

Step out of medieval times and into the modern age with Insight Genesis.

For more information about Insight Genesis watch the video below and visit the website at


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