Scientific term for a white dwarf that periodically erupts and brightens due to mass-transfer from a companion:

Supernova is the term used by astronomers to describe when a star explodes due to mass transfer from a companion. In addition, supernova causes a star to emit its maximum brightness in such a way that its mass is completely ejected from the star's core. 

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