Example 15. Gridding data with large unconstrained regions can cause problems. There are several techniques that can be used in GMT; this example illustrates some of them. Lower left panel shows contours of the surface generated with nearneighbor based on available ship bathymetry. Being a local procedure it will not extrapolate the surface far away from the control data. surface, on the other hand (lower right), will. One can deal with this by either imposing a clip mask based on the data distribution (upper left), or simply overlay the continents to mask out the unwanted contours.