flatland vs plateau

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. 

plateau

noun
  • A largely level expanse of land at a high elevation; tableland. 

  • A comparatively stable level after a period of increase. 

  • A notable level of attainment or achievement. 

verb
  • (of a varying quantity) To reach a stable level after a period of increase; to level off. 

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