Location of the Gulf of Guinea in the region.
The borders of the sea are approximately based on those from the IHO's "Limits of Oceans and Seas" Draft 3rd Edition, 1953, but they're also close to those from the IHO's "Limits of Oceans and Seas" Draft 4th Edition, 2002.
(Winkel III projection centred 0° West and standard parallels at 50°28'.)
The map was created using data from Natural Earth, with mapshaper.  (Natural Earth Data is in the public domain.)  For reproducibility purposes, this was the set of scripts used.

The style of the map was generally intended to follow that of the German Locator maps project, except for the highlight colour of the sea, for which dark blue (#4790c8) was used.
Own work
Aplaice