I have a dataset that includes depth, salinity, sea level, velocity in NetCDF format. Firstly. I need to draw the line between land and sea and then draw velocity on it.I know I have to use the command contour/leves=(a,b,c) depth, I have tried many values for a,b,c but I did not manage to draw the border between land and sea,I would be grateful if you could help me to do it.Kind regards,Pooran