downward vs in vertical extent

downward

adv
  • At a lower level. 

  • Southward. 

  • Toward a lower level, whether in physical space, in a hierarchy, or in amount or value. 

adj
  • Located at a lower level. 

  • Moving, sloping or oriented downward. 

in vertical extent

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