Hydrographic maps reveal subsurface features with the potential to hold fish, the degree to which largely depends on the accuracy and detail of the map. While paper maps are still valuable — I have a file cabinet drawer filled with them — electronic maps on a chartplotter (sonar/GPS unit) have largely replaced them.

Many of the smaller lakes in our state, waters that often provide some of the best fishing, remain unmapped electronically. But more get added periodically. Also, it can get pricey to purchase the most detailed electronic maps, many of which are not part of built in mapping. Fortunately, many modern chartplotters have the ability to create their own custom maps.

All three of the major fishing electronics makers offer units that incorporate their versions of custom mapping programs: Garmin’s Quickdrawn, Humminbird’s Autochart Live and Lowrance’s Genesis Live. Chartplotters equipped with such a feature record depth and GPS positioning information into a data file which is displayed as contour lines in real time. All have the potential of creating maps with 1-foot contours — that’s highly detailed.

While exactly how you get there differs between makers and particular models, generally to start the recording process is simply a matter of selecting the correct menu/submenu and then clicking on the record feature. With Garmin and Lowrance you’ll first need a SD card up to 32 GB. Humminbird units allow a limited amount of recording to internal memory, but you’ll need Humminbird’s Zero Line SD card for anything over a few hours.

Here are a few tips for mapping your favorite locations:

The accuracy and detail of a custom map relies on the effort you make in creating it. On larger bodies of water, consider mapping prime structures like shoreline points and flats first. Maybe one or two during each outing. In time you’ll have a complete picture of the lake’s structure.

Smaller lakes, say 200 acres or less, can be mapped in their entirety in a few hours, working your way around the lake in a circular pattern.

The actual process of mapping requires monitoring the screen as the map is created, making subsequent passes of the recording swath that slightly overlap prior ones for a seamless product. Kinda like cutting the grass. For the utmost accuracy, “remap” a spot from a 90-degree angle, so the transducer can record the bottom from that view.

Boat speed is another consideration. I’ve done most of my recording with Garmin’s Quickdraw, which displays a green circle on the screen when the unit has a solid GPS fix and bottom reading. The circle will turn yellow or red if either is compromised. Generally I’ve been able to maintain a green circle at speeds in the 8-to-9-mph range, which hastens the map-making process.

Modern chartplotters feature a vast array of menus and submenus to access their many features.

If a previously recorded map is not showing up, chances are it got turned off at some point. Often it’s just a matter of turning it back on or making it “visible” to restore it.

Depth offset is another worthwhile feature. If the lake you’re mapping is subject to significant depth changes, it’s wise to use the depth offset option each time you’re mapping so “old” mapping and the new stuff merge well. Offset also restores accuracy to the depths of the contour lines.

Depth shading is another cool feature, allowing you to assign particular shades to various depth zones. As such, prominent bottom features like points and humps stand out.

Though not a “setting” issue, another item to consider is map sharing between units.

If you have both a bow and console unit, it’s a big advantage to be able to share maps, including your custom maps, which are typically created from the console. Not all units share maps, and ones that do often require being in a network to do so. Barring sharing/networking capabilities, in some instances you can copy maps from one card to another via a PC, using the second card on your bow unit.

Admittedly, mapping takes some time and cuts into what you might have available for fishing. But besides the long-term benefits, you can also find a lot of offshore cover while mapping. This includes brushpiles, cribs, foundations, rock piles, stumps, bridge abutments, and others, cover options you might never have found if you hadn’t been navigating the lake with your eyes zeroed in on the electronics.

For this reason it’s wise to split the screen, showing both a map and sonar view (side imaging view is especially useful in this scenario). Or utilizing two screens at the console, one for mapping and one for sonar. Dropping icons that suggest what the waypoint represents is extremely helpful when it comes time to revisit the spot.

Another custom mapping advantage is the shared mapping platforms available via all three major electronics makers. This includes Garmin’s Quickdraw Community, Humminbird’s Auto Chart Live Share and Lowrance’s C-Map Genesis Social Map.

You are able to share the maps you created via these platforms. Conversely, you can download maps someone else has made for your own use. All three are free.

Jeff Knapp is an outdoors columnist for the Butler Eagle.