refer vs touch upon

refer

verb
  • To point to either a specific location in computer memory or to a specific object. 

  • To mention (something); to direct attention (to something) 

  • To submit to (another person or group) for consideration; to send or direct elsewhere. 

  • To make reference to; to be about; to relate to; to regard; to allude to. 

  • To place in or under by a mental or rational process; to assign to, as a class, a cause, source, a motive, reason, or ground of explanation. 

  • Required to resit an examination. 

  • To be referential to another element in a sentence. 

  • To direct the attention of (someone toward something) 

noun
  • A blurb on the front page of a newspaper issue or section that refers the reader to the full story inside the issue or section by listing its slug or headline and its page number. 

touch upon

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