expanse vs flatland

expanse

noun
  • A wide stretch, usually of sea, sky, or land. 

  • An amount of spread or stretch. 

flatland

noun
  • Synonym of plain: land of relatively constant altitude, usually exclusive of forests, deserts, and wastelands. 

  • An urban region with many flats or apartments to rent. 

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