downland vs hogback

downland

noun
  • An area of rolling hills (downs), often grassy pasture over chalk or limestone. 

hogback

noun
  • A sharp steep-sided ridge formed by the erosion of tilting strata 

  • A Viking grave marker taking the form of a recumbent monument, generally with a curved (hogbacked) ridge and outwardly curved sides. 

  • A hogframe. 

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