Bathymetric survey, also known as hydrographic topography, is carried out to map the topography and features of the bed of an ocean, lake, river or other body of water.  A subset of topography, which is the study and recordation of the three-dimensional shape of terrain, bathymetry focuses on elevations of land under a body of water as measured from the water’s surface.  Bathymetric surveys provide information about the unique shape and features of submerged terrain, which can be used to develop detailed maps of the riverbed, lakebed, or seafloor.  The tools utilized in this work include real-time GPS location and precise sonar, taken from stable surface platforms such as boats, for depth measurements and locations.  The characteristics of the terrain under a body of water can be represented like standard topographic mapping, with contour elevations and selected depths.