How has gene duplication played a critical role in evolution? see concept 21.5 (page 452)?

Gene duplication played a critical role in evolution in that it produces redundant copies of existing genes, which are then free to mutate and adopt new functions. it is a major mechanism in which new genetic materials are generated during molecular evolution. Gene duplication is important in that it can provide new genetic material for mutation, drift and selection to act upon, which results in specialized or new gene functions.

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