certificate of identity vs travel document

certificate of identity

travel document

noun
  • An identity document issued by a government or international treaty organization to facilitate the movement of individuals or small groups of persons across international boundaries, such as a passport. 

  • An identity document similar to a passport, but which does not confer proof of citizenship from the issuing country. 

How often have the words certificate of identity and travel document occurred in a corpus of books? (source: Google Ngram Viewer )