courtyard vs piazza

courtyard

noun
  • An area, open to the sky, partially or wholly surrounded by walls or buildings. 

piazza

noun
  • A roofed gallery or arcade (for example around a public square or in front of a building). 

  • A public square, especially in Italian cities. 

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