Ocean sediment thickness contours and water depths ranging from 0 – 18,000 meters. These contours were derived from a global sediment thickness grid distributed by the National Centers for Environmental Information (NCEI). The NCEI grid was compiled from various existing sediment thickness maps and drilling cores, and has a cell resolution of 5 arc seconds. Sediment thickness data is typically acquired through two methods. Seismic (or sub-bottom) profile technologies rely on powerful pulses of low-frequency sound which penetrate the substrate and return information about substrate thickness, character, and stratification. The data are collected along transect lines and require interpolation to create comprehensive maps. Sediment thickness is also determined by direct measurement through coring, which provides more detailed information but only at discrete sites. Coring data can also be interpolated to form area maps, and to help interpret the seismic data.