gradate vs mark out

gradate

verb
  • To arrange in order of grades. 

  • To change imperceptibly from one gradation of tone etc. to another. 

  • To bring to a certain strength or grade of concentration. 

mark out

verb
  • to classify 

  • to set the boundaries of an area 

  • to obliterate or cancel with a mark 

  • to distinguish 

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