I am pleased to say I found the original map (see my above post). The reason I did not know about this before is the map does not appear in the US edition (
Wings of the Morning), at least not in the reprints I read. I first read the book (US edition) in a library I visited and found online (
here). Instead, the map was published in the UK edition and reprints under different title (
Rainbow Island). The map has not before (until now by me) been digitised anywhere online. The book seems to have sold better under the US title and the UK edition (especially first edition) is harder to find a physical copy. The map I scanned was from a reprint (undated but likely 1920s) that arrived in my post today.
Whoever drew the Kidd-Palmer maps heavily borrowed or copied the map of Rainbow Island from the UK edition of Tracy's book. There are fairly minor changes. For example, the annotation "ledge occupied" was changed to "Anchorage", while the words "Valley of Death" were removed and replaced with a small drawing of skull or bones.
Even the compass on the maps is almost identical.
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I am interested in the editions and reprints of Tracy's book in regards to the map so will buy more copies of the book. I guess I will end up like
Jerry Fletcher in the film
Conspiracy Theory (1997) who owns dozens of copies of
The Catcher in the Rye.