How do we know what the make-up of air was like in the past?

Iwolud you, but i dont know what you are asking.

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

They don’t store and transmit heredity