Which is the definition of adhesion?

In biology it is when water is attracted or goes towards a most times solid surface

The action or process of adhering to a surface or object.
Adhering def. = gerund or present participle

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