How many independent variables can be tested in a controlled experiment? (A) five
(B) as many as you want
(C) two
(D) one

The answer is D

one independent variable :)

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