Pool vs Swale

Pool

name
  • A civil parish in the Metropolitan Borough of Leeds, West Yorkshire, England, also known as Pool in Wharfedale. 

Swale

name
  • A river, a tributary of the Ure in North Yorkshire, England. 

  • A local government district with borough status in Kent, England, created in 1974 with its headquarters in Sittingbourne and named after the channel 

  • The Swale, a channel between the Isle of Sheppey and the Kentish mainland 

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