Arthur C. Clarke's short novel Dolphin Island is set on an island in the Pacific. Although this Dolphin Island itself is fictitious, the novel includes references to real locations such as Tonga. From information about these real locations, or even about the climate or other facts about Dolphin Island, how much is it possible to narrow down its location? I doubt it'll be possible to identify it with a specific real-life island, but can we at least figure out a rough geographical position, whether it'd be nearer Polynesia or Micronesia or Melanesia or what?
In the Great Barrier Reef, 100 miles east of Queensland, Australia.
Dolphin Island isn't so oceanic as I'd thought - it's pretty close (at least by Pacific Ocean standards of closeness) to the Australian continent.
From Chapter 5:
"Just a minute," pleaded Johnny. "Please tell me where I am. Is this Australia?"
The nurse took her time in answering as she slowly poured a colorless fluid into a measuring glass.
"Yes and no," she said. "This is Australian territory, though it's a hundred miles from the mainland. You're on an island in the Great Barrier Reef, and very lucky to have reached it. Here, swallow this—it doesn't taste too bad."
The distance of a hundred miles is confirmed multiple times by details throughout the novel: in Chapter 7 the Flying Fish "came scudding out of the west at fifty knots, making the crossing from the Australian mainland in two hours", and of course towards the end of the novel Johnny travels due west in a hundred-mile journey to the beaches of Queensland.
As an addendum, several real-life islands are mentioned which some of the novel's characters originally come from:
In Chapter 5:
Nurse, who had informed him that her name was Tessie and that she came from the island of Tonga
Tonga is actually an archipelago with a few dozen inhabited islands, but anyway. Her homeland would then be a few thousand miles east of Dolphin Island.
In Chapter 6, Mick says:
"Oh, no, my people come from Darnley Island, up in the Torres Strait. They moved here five years ago, when I was twelve. The pay was good, and it sounded interesting."
Mick's family name is Nauru, which is also the name of another Pacific island country. But this one is many thousands of miles away from any of the other islands mentioned, way up to the northeast, so it might be just an Easter egg rather than reflecting any Nauruan heritage of Mick's family.
It's also worth noting that the story of Mary Watson, which in the novel is a folk tale of Dolphin Island, is a true story, but in reality it took place on what's now called Watson Island, only about 20 miles off the Australian mainland, rather than the fictional Dolphin Island. Clarke adds a note about this at the end of the novel:
The story of Mary Watson in Chapter 13 is perfectly true, and I have changed neither names nor dates. However, her tragic adventure occurred not on my imaginary Dolphin Island, but on Lizard Island, much nearer to the mainland.