pornographic literature vs pornography

pornographic literature

pornography

noun
  • The depiction of (non-sexual) subject matter so that it elicits feelings analogous to erotic pleasure; any such depiction. 

  • The graphic, detailed, often gratuitous depiction of something. 

  • The explicit literary or visual depiction of sexual subject matter; any display of material of an erotic nature. 

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