art gallery vs piazza

art gallery

noun
  • A room, group of rooms, or other space where works of art are placed on display, possibly for sale. 

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 art gallery and piazza occurred in a corpus of books? (source: Google Ngram Viewer )