Mainland vs Principality

Mainland

name

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

  • 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. 

Principality

name

  • Wales 

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