Hello Steve, Thank you for reply for the depth problem. I have another problem. In the present set of dataset, the latitude varies from 1N to 180N rather than -90 to 90. I have tried several ways to change the axis in define command line, but it does not work except "define axis/y=1:180:1/~~~". Do you know how to shift the axis to -90 to 90 or 90S to 90N. Thanks alot. Have a nice day.