Middle America vs heartland

Middle America

name
  • A portion of the United States comprising rural and suburban areas, and the mindsets of these areas. 

  • The Midwestern United States. 

  • The American middle class. 

  • A geographical region comprising Mexico, Central America and the Caribbean 

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 Middle America and heartland occurred in a corpus of books? (source: Google Ngram Viewer )