Letchworth Garden City vs Sound

Letchworth Garden City

name
  • Synonym of Letchworth, Hertfordshire, England. 

Sound

name
  • Synonym of Plymouth Sound, Devon, England. 

  • The strait that separates Zealand (an island of Denmark) from Scania (part of Sweden); also sometimes called by the Danish name, Øresund. 

How often have the words Letchworth Garden City and Sound occurred in a corpus of books? (source: Google Ngram Viewer )