The chart datum is the level of water that charted depths displayed on nautical charts are measured from. It has been suggested that this article or section be merged with Geodetic system. ... Portion of chart of Bering Strait, site of former land bridge between Asia and North America. ...

Chart datum is height of water at the lowest spring tide. This is known as the lowest astronomical tide. Lower tides may occur due to meterological effects, such as high pressure systems. The tide is the regular rising and falling of the oceans surface caused by changes in gravitational forces external to the Earth. ... Pressure (symbol: p) is the force per unit area acting on a surface in a direction perpendicular to that surface. ...

Charted depths and drying heights on nautical charts are given relative to chart datum. Tide tables give the height of the tide above chart datum. This makes it possible to calculate the depth of water at a given point and a given time by adding the charted depth to the height of the tide. To calculate whether an area that dries is under water, subtract the drying height from the height of the tide. On a nautical chart, the Drying height is the vertical distance of the seabed that is exposed by the tide, above the level of the sea at the lowest astronomical tide. ... Portion of chart of Bering Strait, site of former land bridge between Asia and North America. ... A tide table is used for tidal prediction and shows the daily times and height of high water and low water for a particular location. ...