flea market vs shopping centre

flea market

noun
  • A permanent indoor market of stalls in a warehouse selling inexpensive antiques, outdated goods, curios, etc. 

  • An outdoor temporary market selling inexpensive antiques, curios etc. 

shopping centre

noun
  • A large retail outlet consisting of several shops. 

How often have the words flea market and shopping centre occurred in a corpus of books? (source: Google Ngram Viewer )