Baselines of the Territorial Sea

Charts and maritime enforcement

According to Charts and Nautical Publications Regulations, 1995, made under the Canada Shipping Act, 2001, all ships navigating in Canadian waters must carry the most up-to-date CHS nautical charts.

In fact, CHS nautical charts are often used in court cases involving violations of Canadian laws in sovereign waters. Because CHS charts establish the Territorial Sea Baseline and show Canada's maritime limits:

  • Canadian law enforcement agencies rely on them to apprehend ships in violation of Canadian maritime law
  • courts of law accept them as evidence of the information therein provided

CHS uses hydrographic surveys and features along the coast to define the baselines of the territorial sea.

The normal baseline of the territorial sea is determined using appropriate points along the low water line of the coast. Straight baselines can be drawn joining appropriate points along a deeply indented coastline or fringe of islands along the coast in its immediate vicinity. Where appropriate, lines drawn using a combination of both methods can be used.

Normal baseline points are called "normal" because they follow the natural coastal landscape. They can be selected on capes, headlands and islands, but are most often located on low-tide elevations (rocks, reefs, drying sandbanks or the limit of the low-water line). Low-tide elevations are above water at low tide and lie within 12 nautical miles of the coast or major islands.

CHS charts indicate where these low-water line points are located since the charts’ vertical datum is the lower of either the low-water line from large tides or the lowest normal tide. This zero level of the charts applies to water depths and is referred to as chart datum. All water depth measurements collected during hydrographic surveys are reduced to the chart datum before being included in the chart.

With Canada’s irregular coastline, however, “straight” baselines are also used to preserve the general trend of the coastline, to close legal bays and mouths of rivers, or to define a fixed limit in a very dynamic environment (like a delta). Straight baselines can only be drawn from capes, headlands, islands and low-water elevations that support a construction permanently above water (like a lighthouse). Lines joining the turning points of straight baselines are geodesics (the shortest distance between two points on the surface of the Earth).

CHS is the custodian of baseline data derived from surveys and charts. However, changes to the baseline of the Territorial Sea can only be made on the recommendation of the Minister of Foreign Affairs and International Trade. The Territorial Sea Baseline is published in regulations, made by the Governor in Council pursuant to the Oceans Act.