It is called the scale ruler.
A map scale lets you convert map distance to ground distance.
A map scale lets you convert map distance to ground distance.
A map scale lets you convert map distance to ground distance.
A map scale lets you convert map distance to ground distance.
A map scale lets you convert map distance to ground distance.
A map scale lets you convert map distance to ground distance.
A map scale lets you convert map distance to ground distance.
A map scale lets you convert map distance to ground distance.
A map scale lets you convert map distance to ground distance.
A map scale lets you convert map distance to ground distance.
A map scale lets you convert map distance to ground distance.
A map scale lets you convert map distance to ground distance.