Mapping Contour Mapping

Contour mapping displays underwater terrain on your chartplotter as contour lines — lines connecting points of equal depth, similar to how topographic maps show elevation on land. Each contour line represents a specific depth, and the spacing between lines indicates the steepness of the bottom. Lines close together mean a steep drop; lines far apart indicate a gradual slope or flat area.

Contour maps are fundamental tools for finding fish-holding structure. Channel edges, creek channels, submerged points, humps, saddles, and drop-offs all become visible on a detailed contour map, allowing you to identify promising fishing locations before you ever reach them. Experienced anglers study contour maps of unfamiliar lakes to develop a fishing strategy, identifying likely areas to investigate based on structural features visible in the contour data.

Contour detail varies dramatically depending on the mapping source. Basic pre-loaded maps may show contours at 10-foot intervals, which misses most subtle structural features. Premium mapping chips from Navionics, LakeMaster, and Garmin LakeVü offer 1-foot contour intervals on many lakes, revealing small humps, ledges, and channel swings that 10-foot contours hide entirely. The difference in fishing utility between 10-foot and 1-foot contours is substantial.

Many modern fish finders also offer real-time contour mapping, where the unit builds custom contour maps from your own sonar data as you drive over the water. This feature is invaluable on poorly mapped lakes, private ponds, and newly flooded reservoirs where commercial mapping data is unavailable or inaccurate.