Data imported from the NOAA Grid Extract webpage (https://www.ncei.noaa.gov/maps/grid-extract/). To prepare data from NOAA, fill the custom grid form, and choose "XYZ (lon,lat,depth)" as the "Output Grid Format", "No Header" as the "Output Grid Header", and either of the space, tab or comma as the column delimiter (either can be used, but "comma" is the default import format of read.bathy). Choose "omit empty grid cells" to reduce memory usage.