piazza vs plaza

piazza

noun
  • A public square, especially in Italian cities. 

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

plaza

noun
  • A town's public square. 

  • A shopping mall. 

  • A strip mall. 

  • An open area used for gathering in a city, often having small trees and sitting benches. 

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