Indian subcontinent vs South Asia

Indian subcontinent

name
  • The landmass south of the Himalayas projecting into the Indian Ocean, sometimes also including nearby islands; the land on the Indian plate. 

South Asia

name
  • All the countries of the Indian subcontinent (principally India, Pakistan, Bangladesh, Nepal, and Bhutan) and the Indian Ocean (principally Sri Lanka, Maldives) 

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