The system will dilate the pupil when the retina is not receiving enough light, and the system will constrict the pupil when too much light hits the retina.

He should put sand around the spill in order to contain it so that it won't spread

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