It is called the scale ruler.
It is the 'scale factor'
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.
That is the scale of that map.
The map key or scale.
The map key or scale.
It is called the scale ruler.