What is the term "chart datum" used to describe?

The term "chart datum" is used to describe a reference point for measuring depths and heights on nautical charts. It serves as a baseline from which various features on a chart, such as water depths and elevations of landforms, are calculated. Chart datum is crucial for safe navigation, as it allows mariners to understand the actual depth of water over underwater features and helps avoid grounding or other navigational hazards.

By using a consistent reference point, navigators can interpret chart information accurately and make informed decisions about vessel operation in relation to the surrounding environment. Understanding chart datum is essential in ensuring that the measurements taken on charts correspond to real-world conditions, thereby facilitating safer passage and navigation in maritime activities.