Tidal Datum Abbreviations on Nautical Charts

Codes identifying standard reference levels used for charted depths and heights.

Common examples include CD for chart datum, LAT for lowest astronomical tide, HAT for highest astronomical tide, MHWS and MHWN for mean high water springs and neaps, MLWS and MLWN for mean low water springs and neaps, MSL for mean sea level, HW for high water and LW for low water. The datum must be identified before a charted height or depth is interpreted.