Andy, yes, that are all solutions I know of. Of course, you assume that the earth is flat in the formula, but I couldn't do better and that's close enough.
For those who don't do formulae (formulas?): Take fleetwood's solution and allow also circles around the south pole with 1/2 (1/3, 1/4,...) ml circumference around the south pole and then you'll see that you start a bit more than 1 ml north of the south pole, make 1, 2, 3, 4, ... full circles around the pole (the nearer you are, the sillier you feel) to cover one mile and walk the first mile back north.

New puzzle: How long is the shortest word in a Latin script Eurpoean language that has all five vowels (aeiou) in it?

Wolfgang