subsurface vs surface area

subsurface

noun

  • A surface which is a submanifold of another surface. 

  • Something that is below the layer that is on the surface. 

adj

  • below the surface 

surface area

noun

  • The total area on the surface of an object. 

  • The total resources of a system that are accessible from the outside world and thus might be attacked. 

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