A bathymetric chart is the submerged equivalent of an above-water topographic map. Bathymetric charts are designed to present accurate, measurable description and visual presentation of the submerged terrain. In an ideal case, the joining of a bathymetric chart and topographic map of the same scale and projection of the same geographic area would ...
A map delineating the form of the bottom of a body of water, usually be means of depth contours ( isobaths ). 
A topographic map of the earth's surface underlying a body of water (such as the ocean floor).
bathymetric chart A topographic map of the floor of the ocean.