BlueTopo is a compilation of the nation's best available bathymetric data. Created as part of the NOAA Office of Coast Survey's nautical charting mission and its National Bathymetric Source (NBS) program, BlueTopo is curated bathymetric source data to provide a definitive nationwide model of the seafloor and navigational lakes. In the same way that a topographic map details the height of land, BlueTopo details the depth of lake beds and seafloor beneath navigationally significant U.S. waters. Primary sources of bathymetry in NBS compilations include NOAA and U.S. Army Corps of Engineers hydrographic surveys and topographic bathymetric (topo-bathy) lidar (light detection and ranging) data. Data submitted through the NOAA Office of Coast Survey's external source data process are also included. Coverage gaps in water over 200 meters are filled in BlueTopo through Global Multi-Resolution Topography, a merged model of bathymetry made available through Lamont-Doherty Earth Observatory. In addition to compiled bathymetry, BlueTopo contains metadata with quality metrics from the source data to enable the appropriate use of the product.