Suppose that 30% of a molecule of dna is composed of adenine bases (a) and 20% is composed of guanine bases (g). what percentage of cytosine and thymine bases would that same dna molecule have? explain your reasoning.

Thymine simply would have 30% and Cytosine would have 20%. You must remember the pairings! (A-T;C-G) Except in RNA (if you've learned that, Uracil replaces Thymine; pairing with Adenine.

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