An allele hidden by another allele that appears least often in offspring is known as what?

That is known as the recessive allele. 

C. gemstones they are the only non metallic mineral from the list.

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