Mario Capecchi, Sir Martin Evans, and Oliver Smithies recently won a Nobel Prize for gene targeting (gene knockouts) in mice. Describe the steps involved in creating a knockout mouse.

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

Google - what is the first three eras within the phanerozoic eon