mean sea level

Mean sea level (MSL) is the average height of the ocean's surface over a long period, accounting for variations caused by tides, currents, and weather. It serves as a standard reference point to measure land elevations and depths, allowing for consistent comparisons worldwide. MSL is not a fixed point; it fluctuates with natural and climate-related changes, but averaging these changes over time provides a stable baseline for mapping and construction. Essentially, MSL is the baseline used to determine how high or low land and underwater features are relative to the ocean's average surface.