Bathymetry is the measure of depth of water in oceans, seas, lakes, and rivers. Bathymetry data is used to create maps (called "charts") of the seafloor. Bathymetric charts are the equivalent of topographic maps on land.
In the past, the depth of water was measured by lowering weighted lines overboard.
Sonar invented in the 1920s and works by reflecting sound waves off the ocean floor. SONAR (short for "SOund NAvigation & Ranging") is a system for detecting objects under water and for measuring the water's depth by emitting sound pulses and detecting or measuring their return after being reflected off the seafloor.
Major provinces of the ocean floor
• Continental margins - these are regions that extend from the coast across shallow shelf regions to the edge of continents where the seafloor descends into deep water.
• Deep-ocean basins - This includes parts of the oceans where deep water prevails. Deep ocean basins cover the greatest portion of the Earth's surface.
• Oceanic (mid-ocean) ridges - nearly 12,000 miles (20,000 km) of mountain belts run through ocean basins and are associated with divergent plate boundaries (spreading centers).
Each of the major provinces are discussed in detail in the next sections.