inner city vs terrain

inner city

noun
  • The interior, central part of a city, as opposed to the suburbs 

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 inner city and terrain occurred in a corpus of books? (source: Google Ngram Viewer )