The length of a degree is in a ratio to the radius of a circle.

(The centre of the circle is the eye! The viewing device).

Whatever length of unit is used to define one, equally dictates the other.

Earths radius of 3963 miles produces a degree length of 24887.64 ÷ 360 = 69.13 miles.

This is equivalent to a ratio of radius : degree is as 57.3248 : 1.

And a circumference of 360 units.

Ratio = 57.3 : 1

This ratio applies to all circles.