Longitude

[Murthy Yenamandra]

Joe Varo writes:
> Another question:  is the nautical mile part of the metric system?  Do
> pilots from countries other than the US reckon their distances in
> kilometers or nautical miles?  Is the kilometer, for some reason, equally 
> accurate over both land and sea?

The goal is convenience, not accuracy or precision (a mile, kilometer or
a nautical mile can be as accurate or precise as you want to make them).
The nautical mile is a convenient unit as long as we measure latitude
and longitude in degrees and minutes. It's a little misleading (think of
it as the "nautical distance unit" instead) and has nothing to do with
the regular mile and it is convenient only on the sea because you don't
have to worry about the topography.

A metric unit is not needed unless you want to measure latitude and
longitude in metric using gradians, radians or some such units (which is
not a popular practice), in which case nautical miles defined using
minutes of the arc are no longer convenient. The nautical mile is not
part of the metric system, but is an international unit nevertheless and
can be used whether your normal unit of choice is the mile or the
kilometer. In the electronic age, it doesn't really matter which unit
you want to use since you don't have to do the converting multiplication
and division manually.

Murthy

-- 
Murthy Yenamandra, Dept of CompSci, U of Minnesota. mailto:yenamand at cs.umn.edu
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