continuous tense vs present imperfect

continuous tense

noun
  • A verb tense expressing ongoing action; in English, any of the tenses formed with the present participle, namely present continuous ("I am dreaming"), past continuous ("I was dreaming"), present perfect continuous ("I have been dreaming"), past perfect continuous ("I had been dreaming"), future continuous ("I will be dreaming") or future perfect continuous ("I will have been dreaming"). 

present imperfect

noun
  • A grammatical tense which presents the action in the present as continuous, not yet over 

How often have the words continuous tense and present imperfect occurred in a corpus of books? (source: Google Ngram Viewer )