courtyard vs playground

courtyard

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

playground

noun
  • A large open space for children to play on, usually having dedicated play equipment (such as swings and slides). 

  • Any physical or metaphysical space in which a person or organization has free rein to do as they please. 

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