The level to which both tidal levels and water depths are reduced - on most UK charts this level is approximately the predicted lowest astronomical tide level (LAT).
The water level used to record data on a chart. Usually the average low tide water level.
The datum to which soundings on a chart are referred. It is usually taken to correspond to a low-water elevation, and its depression below mean sea level is represented by the symbol Z . Since 1989, chart datum has been implemented to mean lower low water for all marine waters of the United States, its territories, Commonwealth of Puerto Rico, and Trust Territory of the Pacific Islands. See datum and National Tidal Datum Convention of 1980.
The level of the lowest tide there has ever been at a particular place. All depths on a chart and heights of tide refer to it. Search for more information...
The datum or plane of reference to which all depths and drying heights on a chart are related (this does not include other heights and elevations). It is a level so low that the tide will not frequently fall below it. Usually defined in terms of low-water level such as LAT. Chart datum is not a horizontal surface, but may be considered as such over a limited local area. Chart datum should preferably be the same as the datum of tidal predictions for an area.
The water level used to calculate the water depths that are shown on "navigation charts" and are a reference point for harbour and channel dredging. ( zéro des cartes)
Chart datum is the low water plane, below which depths on a nautical chart are measured and above which tidal levels are sometimes measured.
A plan below which the tide will seldom fall. The Canadian Hydrographic Service has adopted the plane of Lowest Normal Tides (LNT) as chart datum. To find the depth of water, the height of tide must be added to the depth shown on the chart. Tidal heights preceded by a (-) must be subtracted from the charted depth. Note: United States tidal datum is Mean Low Water and can differ from Canadian datum by as much as 1.50 metres.
the reference, or "0," water level on a nautical chart. Usually set at the level of mean lower low water.
(or datum, datum plane, hydrographic datum, plane of reference, reference plane, tidal datum, tidal datum plane). The permanently established surface from which soundings or tide heights are referenced (usually low water). The surface is called a tidal datum when referred to a certain phase of the tide. In order to provide a factor of safety, some level lower than mean sea level is generally selected, such as mean low water or mean lower low water.
The plane or level to which SOUNDINGS, tidal levels or WATER DEPTHS are referenced, usually low water datum. See also DATUM PLANE and REFERENCE PLANE.
The datum to which soundings on a chart are referred. It corresponds to the low-water datum (LWD) elevation.
the level below which soundings are given on some charts and maps above which are given the drying heights of features. Datum is also the level above which tidal levels and predictions are given in Tide Tables.
The datum to which levels on a nautical chart and tidal predictions are referred; usually defined in terms of a low-water tidal level, which means that a chart datum is not a horizontal surface, but it may be considered so over a limited local area.
The chart datum is the level of water that charted depths displayed on nautical charts are measured from. The chart datum is generally a tidal datum; that is, a datum derived from some phase of the tide. Common chart datums are lowest astronomical tide and mean lower low water.
