This is a discussion of the County of Cornwall with mentions of topography found in the Poldark series. It was may have been written by Winston Graham; but it doesn't have anything to do with the series.
I had hoped for more. "Poldark" is in the title, but the romance of the series is not in the book. Bottom line: much of the series is fictional, and cannot be found in reality, or on any map.
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Poldark's Cornwall