QUESTIONS !
Décrivons la granulométrie en amont en aval de chaque bagage

Is this what you want me to answer?
I will try my best.
Comment

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