You can "draw" electronic pictures of different bottom structures, including channels, humps, points, reefs and the like, and also outline major cover such as a large weed bed. Set your unit to an appropriate scale. For example, you wouldn't use an 8-mile scale to trace a structure encompassing a few hundred feet. A .15- or even .1-mile scale would be best to enlarge the area for more detail. You'll temporarily lose the overview background map, but any icons or waypoints you placed will remain. Use your sonar to run the weed edge or structure. Your GPS will automatically trace the object. Drop icons (I use an "X" icon) at significant spots like turns or changes in bottom. When you've finished mapping, save your trail (the outline) and name it on the machine. Go back and concentrate on fishing the outlined area. Turn off the plotter trail view to avoid confusing, overlapping lines. When you get a bite, drop fish icons to complete the data bank for the spot.