Which best describe the structure of dna?
a.) purine backbones with pyrimidines on the inside.
b.) base backbones with sugar on the inside.
c.) sugar-phosphate backbones with bases on the inside.
d.) a backbone of bases with phosphate groups on the outside.

A double helix structure, with a sugar phosphate backbone, and nucleotides. 
Nucleic acids arranged in a double helix ITS C NOT D 

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