Ellen has it right. Latitude is measured from the equator.
Lines can there for be parallel and equally spaced. One
minute of longitude will vary by the distance to the equator.

However, if you follow a line of latitude around the earth
the length is a function of latitude. i.e. at 60 deg South it
is quicker than at the equator.

Longitude lines are all the same lenght and converge.

"Dave" wrote

"Bart Senior" .@. said:
How long is a minute of Longitude--at your Latitude?
And what is the formula to calcuate it?

I think you got that backward, Bart. A minute of Longitude is always 1 NM.
That's why you always measure distance by going to the side of the chart
rather than the top or bottom. It's the length of a minute of latitude
that
varies with what latitude you're at, getting shorter as your latitude
increases from the equator.