airport vs heliport

airport

noun
  • An airfield (an area designated for the takeoff and landing of aircraft), including one or more runways and (for commercial airports) one or more passenger terminals. 

heliport

noun
  • A facility, such as a small airport, designed to let helicopters take off and land. 

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