How To Read Nautical Charts | Garmin Blog

Fish and Hunt Marine Understanding your nautical charts November 19, 2025

When you’re on the water, you have to pay attention to navigation aids such as lights, buoys, channel markers and more. Whether you need a standard navigation chart to get where you’re going or relief shading for your favorite marine activity, Navionics® mapping from Garmin is a trusted travel tool.

You’ll be able to flip back and forth between some or all of the following layers to get the perfect view for the journey ahead from your compatible chartplotter or on your smartphone via the ActiveCaptain® or Navionics® Boating app.

Navigation chart

With this chart layer, you’ll get an overhead view of buoys, lights, cables, depth soundings, marinas, tide stations and more so you can navigate with confidence. Hover over the symbols to learn more about what each data point represents.

Chart detail varies depending on the zoom level so you can see the most important and appropriate information without clutter. You can adjust your chart settings for your preferred setup.

Fishing chart

When looking at the fishing map, you’ll see detailed bottom contour lines. Each line represents depth level, which is great for identifying fish structure (like points, humps and drop-offs) and knowing when you’re approaching shallow waters.

Contour lines that are further apart indicate little change in depth, while those closer together indicate a steeper change.

To contribute to depth data that can be used to improve map detail, check out the Garmin Quickdraw™ Contours feature on your Garmin chartplotter.

Relief shading chart overlay

Relief shading gives boaters high-resolution imagery of lake and coastal waters for a clear view of changes in depth that can reveal the underwater landscape. Color and shadow represent different depths, with shallower waters appearing red transitioning to deepest waters appearing dark blue and purple.

Those varying colors and shadows make it easier to spot depth changes, channels, flats, sunken ships and reefs.

Satellite imagery chart overlay

For improved situational awareness and a realistic view of your surroundings, activate a high-resolution satellite imagery overlay. Satellite imagery makes it easier for you to spot onshore features such as marinas, boat ramps and coves.

Sonar imagery

Seeing bottom hardness through sonar imagery is helpful for adjusting fishing strategies and solidifying what species you might find. Available on select lakes, this view reveals bottom hardness in color to highlight both subtle and dramatic changes through sonar echo returns.

Stronger echo returns indicate rocks, trees, roads and creek banks, all having the potential of attracting fish. Harder bottoms will be shown through lighter colors, such as light orange and yellow.

Weaker returns typically indicate softer bottoms, such as mud or sand, and will be shown using darker colors, such as orange to reddish brown. When you’re trolling in this color, you’re bound to reel in catfish or bass.

3D View

Great for seeing above and below the waterline, two 3D options include both MarinerEye and FishEye perspectives. Locate potential fishing and diving locales by viewing the depth and elevation around your boat. Plus, identify potential hazards and see upcoming harbors and ports when using MarinerEye.

ActiveCaptain® Community

The ActiveCaptain Community is a great source of local knowledge contributed by boaters. Included are points of interest that users have uploaded, including ratings, photos and reviews of marinas with fuel prices and amenities, as well as local condition changes, new hazards and more.

Customize your maps to make them as simple or advanced as you’d like. Learn more about Garmin Navionics and browse our collection of chartplotters to help improve your next boating excursion.