ground plan vs undirected graph

ground plan

noun
  • A diagram showing set layout. 

  • Framework or pattern. 

  • Hypothetical ancestor of a clade. 

  • Floorplan. 

undirected graph

noun
  • A graph in which the edges are not ordered, so the edge (a, b) is identical to the edge (b, a). 

How often have the words ground plan and undirected graph occurred in a corpus of books? (source: Google Ngram Viewer )