[throwawaylinux]

Ah, good point. In that case expand the niche cases to traveling due north or south.

[jabl]

In practice, when navigating by pen and paper, what you do is you measure a distance on the chart with a divider, then you put the divider (with the previously measured distance set) to the north-south scale on the side of the chart to read out the distance in nautical miles.

Now, of course, in principle charts could have a separate scale for distances in km, and we could use km for navigation just fine. But, well, I've never seen a nautical chart with such a scale.

[wkat4242]

And, at sea level. At altitude this no longer applies either because the circumference at altitude is greater.

[closewith]

Well, it still applies in aviation, as distance and ground speed used in navigation are measured at sea level irrespective of altitude.

[pbmonster]

...by around 0.1%. Which is why nobody is bothering with it, considering how susceptible to wind speed distances and velocities are up there.