Idea

I think that would be great to add polygons (with a code) for the oceans and seas. This way I could a make a map of the Mediterranean Sea (MS) with a code like -R=MS (or -R=MediterraneanSea).

Proposal

We could follow "Limits of Oceans and Seas" of the International Hydrographic Organization (1953) to avoid any definitions or naming issue. There is a draft for the a new version but it is not official yet.

The limits of IHO (1953) were digitized (in shp fles) and adapted to the GSHHS by Fourcy and Lorvelec (2013). In its website they said that: "This map is freely available for non-commercial use".

The shp file (153,8 MB) contains 105 objects but are many polygons that correspond to sub-divisions (like all the seas of the Mediterranean) and sub-sub-divisions that we could exclude (or not). Or maybe include just some of the same (like the states of the larger countries).

The main divisions are only 9/10 (see southern ocean below).

1. North Atlantic Ocean
2. Baltic Sea
3. Mediterranean region
4. South Atlantic Ocean
5. Indian Ocean
6. South China & Eastern Archipelagic seas
7. North Pacific Ocean
8. South Pacific Ocean
9. Arctic Ocean
10. Southern Ocean

Here is a map from the shp file:

gmt plot -Rd -JW15c HRmLOS_1.1.shp -Bf -png Oceans3 -Gdodgerblue2 -W

Souther Ocean

The main issue would be the southern ocean which: "The IHO included the ocean and its definition as the waters south of the 60th parallel south in its 2000 revisions, but this has not been formally adopted, due to continuing impasses about some of the content, such as the naming dispute over the Sea of Japan."
For example, here in the NOAA it was included.

References and source

• "Limits of Oceans and Seas, 3rd edition" (PDF). International Hydrographic Organization. 1953. Link
• Fourcy, Damien; Lorvelec, Olivier (2013). "A New Digital Map of Limits of Oceans and Seas Consistent with High-Resolution Global Shorelines". Journal of Coastal Research. 29 (2): 471–477. doi:10.2112/JCOASTRES-D-12-00079.1. Researchgate Link