What is the unique thing about stem cells that makes them so desirable

Stem cells are so desirable because they can turn into any other kind of specified cell in the body, such as it can become a brain cell, tissue cell, muscle cell etc.

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