Ptolemy could not explain without epicycles and deferents.

Ptolemy could not explain * Retrograde motion of the planets* with out epicycles and deferents.

They must use the scientific method

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