What are lines called that connect points of equal depth on nautical charts?

The lines that connect points of equal depth on nautical charts are referred to as "bottom contours." These lines help mariners understand the underwater topography, providing essential information about the seabed. By visualizing these contours, navigators can ascertain safe passage depths, identify underwater hazards, and make informed decisions regarding route planning.

In the context of nautical charts, bottom contours serve a crucial role similar to that of contours in land-based topographic maps, but they are specific to underwater environments. This terminology is important, as it highlights the features unique to marine navigation. Understanding bottom contours is vital for effective navigation, especially in shallow or complex waters where depth variations can pose significant risks.