orography vs terrain

orography

noun
  • the orographic features of a region 

  • the scientific study, or a physical description of mountains 

terrain

noun
  • An area of land or the particular features of it. 

  • The surface of the earth; the ground. 

  • A single, distinctive rock formation; an area having a preponderance of a particular rock or group of rocks. 

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