Hydrographic surveying analyzes the sea and ocean to see what the floor looks like. It describes and measures the physical features of the navigable portion of the surface and coastal areas, in relation to the use for the purpose of navigation. Hydrographic surveying uses echo sounding to determine water depths and depths of the sea bed at different locations. To locate location, GPS receivers and RTK receivers are used.
During the survey, speal attention is paid to locate the least (shoalest) depths, to warn mariners of dangers to navigation. Tides and water level measurements are recorded to provide a vertical reference for water depths.
During the survey, floor materials - like sand, mud and rock - are recorded. This can be important for dredging, anchoring, dredging, pipeline routing, cable routing and more.
Results are drawn on a nautical chart. Nautical charts are not regular maps. Regular maps concentrate on land areas, landmarks, roads, railways, etc., whereas nautical charts show details of water areas.