ETOPO1 was built using GMT 4.3.1 (http://gmt.soest.hawaii.edu/), development version/CVS. GMT 4.3.1 creates grids in netCDF COARDS-compliant format. This is the format of the "gmt4" version in this directory, and is recommended for GMT 4 users. Some older versions of GDAL (http://www.gdal.org/) do not properly read the netcdf grids created by GMT 4 (grids are inverted south to north). If you are using an older version of GDAL and encounter this problem you can work around the problem a couple different ways. If you have a version of GMT installed, you can reformat the netcdf grid to a depreciated netcdf file that older GDAL will read correctly, you can do this with the following command: $ grdreformat Etopo1_gmt4.grd Etopo1_gdal.grd=cf Another option would be to obtain the geotiff version of ETOPO1, found at the following address: http://www.ngdc.noaa.gov/mgg/global/global.html Newer versions of GDAL should correctly read the gmt4 netcdf grids. Please contact me if you have problems with ETOPO1. Barry W. Eakins barry.eakins@noaa.gov ETOPO1 1 Arc-Minute Global Relief Model http://www.ngdc.noaa.gov/mgg/global/global.html