A chart datum is the water level surface serving as origin of depths displayed on a nautical chart and for reporting and predicting tide heights. A chart datum is generally derived from some tidal phase, in which case it is also known as a tidal datum.[1] Common chart datums are lowest astronomical tide (LAT)[1] and mean lower low water (MLLW). In non-tidal areas, e.g. the Baltic Sea, mean sea level (MSL) is used.[2] A chart datum is a type of vertical datum and must not be confused with the horizontal datum for the chart.
- ^ a b Australian Bureau of Meteorology National Tide Centre Glossary (retrieved 30 April 2013)
- ^ Sjofartsverket: Mean Sea Level