Mainland vs South Island

Mainland

name
  • The largest island in the Orkney Islands council area, to the north of Scotland. 

  • The largest island in the Shetland Islands council area, to the north of both Orkney and Scotland. 

  • A historical region in British Columbia, British North America, British Empire 

South Island

name
  • An island, the southern of the two major islands making up New Zealand. 

How often have the words Mainland and South Island occurred in a corpus of books? (source: Google Ngram Viewer )