Frequency is
a. the number of waves that pass a point in a given time
b. the height of a wave
c. the speed of a wave
d. the length of a wave

the rate at which a vibration occurs that constitutes a wave, either in a material (as in sound waves), or in an electromagnetic field (as in radio waves and light), usually measured per second.

A. the number of waves that pass a point in a given time

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