picket fence vs railing

picket fence

noun
  • A simple fence made from wooden pickets, connected by horizontal bars. 

  • A series of spaced perpendicular striations that occasionally occur in aurorae. 

railing

noun
  • A fence or barrier consisting of one or more horizontal rails and vertical supports. 

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