If two erminette chickens were crossed, what is the probability that: a. their offspring would be black? b. their offspring would be white? c. their offspring would be erminette?

Very hard to understand

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