I'm afraid that an important point (I think) was lost in the
discussions about a relatively minor (and maybe unnecessary)
digression I made from the main thought about map scales and nautical
miles.
On 2007 Mar 6 , at 8:54 AM, John M. Steele wrote:
Just a comment on your calculation. The legal definition of the
nautical mile in the US is 1852 m, since 1954.
Several people have informed me of this fact. The figure of 1852 m is
the official definition but it does not correspond to the original
intent of the nautical mile as being equal to the distance
corresponding to 1 minute of longitude or latitude at the equator. So
what?
That was not the main point.
My main criticism of that original message had to do with the
statement that "it is easy to see that such a scale is not helpful".
(The scale in question was a pure ratio for a map scale instead of
the "1 inch = 20 nautical miles" original scale.) The pure ratio
scale would be useful with any measurement units and therefore, in my
judgement, it was more helpful than the original which was only
helpful for a limited set of units (inches and nautical miles). In my
opinion, it could easily be seen that it WAS helpful and could have
been MORE helpful if the value had been rounded off appropriately.
My digression into questioning the actual value he used was more or
less irrelevant to the main criticism.
The important point was that the value given was not rounded off
reasonably and therefore resulted a very awkward numerical value for
something that looked so much simpler in the old English units of
inches and nautical miles. This is the same argument that is flung at
the metric system when people convert from an old English units to
metric units. They say our old 55 MPH speed limits will become 88.5
km/h, and that the shopper who wants a pound of ground beef will be
required to order 454 grams. They lose sight of the simplicity of the
metric system because of the failure to use reasonable rounding in
any conversions that are made. (There are, of course, some cases
where rounding off is not reasonable, but more often than not, some
rounding is necessary.)
It seemed to me that, in the case of the map scale conversion, the
same thing was happening. They converted exactly and got an awkward
looking number so they concluded that the difficult number was the
fault of the metric system (or in this case, pure ratio form of the
map scale), whereas it is actually the fault of the failure to round
reasonably.
Bill Hooper
75 kg body mass*
Fernandina Beach, Florida, USA
* plus or minus a kilogram or two, and
up 2 kg from what it used to be.
