exterior vs heartland

exterior

noun
  • Foreign lands. 

  • The outside part, parts or surface of something. 

adj
  • Being from outside a country; foreign. 

  • Outdoor. 

  • Relating to the outside parts or surface of something. 

heartland

noun
  • The central part of a region defined by geographical or non-geographical criteria, such as support for a political party, faith or similar. 

  • The part of a region considered essential to the viability and survival of the whole. 

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