What is the baseline for measuring the breadth of a territorial sea?

The baseline for measuring the breadth of a territorial sea is defined as the low-water line as shown on official charts. This line provides a consistent and navigable reference for determining the extent of the territorial sea, which generally extends up to 12 nautical miles from that baseline. Using the low-water line ensures that measurements account for variations in tides and allows for a more uniform and legally recognized demarcation point.

This choice helps establish an internationally recognized and enforceable boundary for coastal states, enabling them to manage marine resources and enforce laws within that jurisdiction effectively. The baseline ensures clarity and reduces disputes regarding territorial claims, which are crucial in international maritime law.

Other options, while they may have relevance in different contexts, do not serve as the standard baseline for measuring the territorial sea. The mean high-water line is not suitable as it fluctuates with tides; the average tide level does not provide a fixed reference point; and the highest point of the coastline does not accurately reflect the boundary used in maritime law.