back forty vs hinterland

back forty

noun
  • The most remote or inaccessible part of any place. 

  • The remote part of a farm. 

hinterland

noun
  • A remote or undeveloped area, a backwater. 

  • The land immediately next to, and inland from, a coast. 

  • Anything vague or ill-defined, especially something that is ill understood. 

  • The rural territory surrounding an urban area, especially a port. 

  • That which is unknown or unexplored about someone. 

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