Free energy is the amount of energy available for the cell to carry out its many chemical processes. it is the difference between the internal energy (or enthalpy) and (or disorder).

The higher you go up the less oxygen there is 

Sorry its not enough info

Are you asking about a street map usage  if so here is your answer  a street map for a very limited area could simply be a bit map or a .jpg image.  but a more general map would probably store the streets as vectors.  but you shouldn't assume that there is one way to do it