collage vs improvisation

collage

noun
  • The technique of producing a work of art of this kind. 

  • A picture made by sticking other pictures onto a surface. 

  • A composite object or collection (abstract or concrete) created by the assemblage of various media; especially for a work of art such as text, film, etc. 

verb
  • To make into a collage. 

improvisation

noun
  • The act or art of composing and making music, poetry, and the like, extemporaneously 

  • That which is improvised; an impromptu. 

  • Musical technique, characteristic of blues music. 

  • The act of improvising, acting or going about something without planning ahead 

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