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.
Crystal Codex 