crosswalk vs grade crossing

crosswalk

noun
  • A point designated for pedestrians to cross a street. 

  • A mapping between equivalent elements (fields) in different database schemas. 

verb
  • To map equivalent elements (fields) in different database schemas. 

grade crossing

noun
  • An at-grade crossing between a railroad line and an ordinary road, with tracks and road at the same level. 

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