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In light of recent events, here's OpenStreetMap editors discussing naming of the Gulf of Mexico
(community.openstreetmap.org)
This is a most excellent place for technology news and articles.
Looking at it this way, I'd call the "mainland" part West Taiwan
Nah West Taiwan is the western half of Taiwan. It's an island, not a state, just as Denmark is not Jutland, or Spain, or Portugal (fight!) Iberia.
You're getting downvoted but you ain't wrong.