Bathymetry, the mapping of the shape of the seafloor, is fundamental to many activities in the ocean. Uncertainty and resolution vary greatly within and between bathymetric maps and grids due to the sparse and irregular distribution of acoustic measurements and the low resolution of satellite data. There is promise of great improvements over the next few years from both new instrument platforms and increased international cooperation and sharing of data. This section describes how bathymetry maps are made and provides guidance on their use.