burgomaster vs city manager

burgomaster

noun
  • The mayor, or head magistrate, of a town in the Netherlands, Belgium, Germany and certain other countries. 

city manager

noun
  • A municipal official responsible for the operations of a city, usually appointed by a town or city council rather than elected. 

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