Now Invert the selection (Select->Invert), create a new black layer called “Land Mask”
and fill the selection with white. Now save the selection to a Channel (Select->Save to
Channel) and rename the channel to “Land Mask”. This will be used a fit bit later.
To make the ocean/water (and the base contour for the land as well) a two layer variant of
the three layer sandwich will be used.
Copy the “Land Mask” Layer, and rename it “Sea Shape”. Apply a Gaussian Blur
(Filter->Blue->Gaussian Blur) large enough to eliminate the absolute black and whites
of the image. In this case, I used the same size as the image (500px).