Glossary of Terms and Abbreviations

This glossary is based in part on Canada's Extended Continental Shelf glossary.

Baselines or coastal baselines: the lines from which the territorial sea is measured. The normal baseline is the low-tide line along a coast. Where a coast is deeply indented and cut into, or there is a fringe of islands along the coast in its immediate vicinity, straight baselines joining appropriate points may be drawn.

Bathymetric survey: an echosounder survey that measures the depth of the water and determines the shape of the seabed. Data from bathymetric surveys create bathymetric maps, the submerged versions of topographical maps.

Coastal baselines: see baselines.

Constraint line: Article 76 of the U.N. Convention on the Law of the Sea provides two constraint lines that are applied against the two formula lines, to ensure the extended continental shelf (ECS) resulting from the formula lines does not extend seaward of the more distant of these two constraint lines. The first constraint line is based on distance, and limits an ECS to 350 nautical miles from a country's coastal baselines. The second constraint line is based on bathymetry and limits an ECS to 100 nautical miles seaward from the 2,500 meter isobath. Like the two formula lines, the constraint lines, in general, can be used in any combination when determining the limits of an ECS. See diagrams of constraint lines.

Echosounder: an acoustic instrument using sound to measure depths to the seafloor. Data from multibeam echosounders are used to create bathymetric maps.

Extended Continental Shelf (ECS): Under international law, as reflected in the U.N. Convention on the Law of the Sea, every coastal country has a continental shelf out to 200 nautical miles (nm) from its coastal baselines, or out to a maritime boundary with another coastal country. However, the continental shelf of a coastal country extends beyond 200 nm (the "extended continental shelf") if it meets the criteria outlined in Article 76 of the Convention.

Exclusive Economic Zone (EEZ): an area beyond and adjacent to the territorial sea, extending up to 200 nautical miles from the baselines, where a coastal country has sovereign rights as set forth in Article 56 of the U.N. Convention on Law of the Sea, such as those relating to natural resources in the water column, on the seabed, and in the subsoil.

Foot of the slope: According to Article 76 of the U.N. Convention on Law of the Sea, the foot of the slope, absent evidence to the contrary, is the point along the base of the slope where the gradient of the seafloor undergoes its maximum change. The foot of the slope serves as the point from which the two formula lines - the sediment thickness formula and the bathymetric formula - are drawn.

Formula line: A coastal nation may use any combination of two formulas provided under Article 76 of the U.N. Convention on Law of the Sea. The sediment thickness formula, (also called the Gardiner formula or Irish formula) relies on a combination of morphology and sediment thickness. It generates a line defined by points where the thickness of the sediment is at least one percent of the distance to the foot of the slope. The bathymetric formula (also called the Hedberg formula) relies on morphology of the seafloor and generates a line defined by points 60 nautical miles seaward from the foot of the slope. A coastal country may use either of these formulas or any combination of them to maximize the extent of its ECS. See diagrams of formulas.

Isobath: a contour line on a map connecting points of equal depth in a body of water.

Nautical mile (nm): 1 nautical mile equals 1,853 meters or 6,080 feet.

Seismic survey: a survey of the seabed using sound waves that are reflected from different layers of material in the subseafloor. Echoes from each layer are detected by hydrophone receivers, and the travel time and speed of sound in different materials provide information about the characteristics of the subseafloor and the depth of sedimentary material.

Territorial sea: an area of the sea not exceeding 12 nautical miles from the baselines where the coastal nation exercises sovereignty, subject to the right of innocent passage and other rules of international law.

United Nations Convention on the Law of the Sea (UNCLOS): an international treaty establishing a legal framework for the oceans. The Convention creates maritime zones such as the territorial sea, the exclusive economic zone and the continental shelf, and sets out provisions governing ocean activities as diverse as navigation, fisheries, marine scientific research and protection of the marine environment.