flatland vs grassland

flatland

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

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

grassland

noun
  • An area dominated by grass or grasslike vegetation. 

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