Given a SINGLE longitude coordinate in decimal degrees, how do I calculate the distance in miles or km between latitude 0 and 1 at that longitude? ie what is the formula?
For example, given 51.43567 longitude, what is the distance between 0 latitude and 1 latitude at that longitude?
Note, that I do not want any radius around the point. Just a single number in miles or km.
EDIT: I posed the wrong question above. The correct one is below. I recognise the mkenndy's answer still points to the correct formula in one way or another, however, I need the point in bold below clearly set out.
Given a SINGLE latitude coordinate in decimal degrees, how do I calculate the distance in miles or km between any longitude at that latitude? ie what is the formula?
For example, without any concept of distance *, given 51.43567 latitude, what is the distance between 1 and 2 longitiude at that latitude?
.* known distances between longitude decimal degrees are only the equator and the poles.
The answer should just be a single number in miles or km.
Please use my example and show clear workings out in your answer to give the answer in miles or km.