Are chemical messengers that are released from the axon terminal to transmit an impulse to the next neuron

Neurotransmitters is the word you're looking for.

Thats bot a question

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