courtyard vs plaza

courtyard

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

plaza

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

  • A town's public square. 

  • A shopping mall. 

  • A strip mall. 

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