If one inch on the map equals about 2.25 miles, then 0.444 inches on the
map equals about 1 mile.  (1 divided by 2.25 equals 0.444).  On the natural
scale indicator, that shows a scale of about 1:145,000.

If the distance on the map is short, say under an inch, it's helpful to
multiply both the distance and resulting NSI result by 10, which makes it
much easier to use the NSI because the scales on the NSI aren't so crammed
together.  For example, 0.444 times 10 is 4.44. If you place the NSI along
a line that's 4.44 inches long, you get a scale of about 1:14,200. Then if
you multiply 14,200 by 10 you get the actual scale of about 1:142,000.

The scale on the record (1:57,217) is clearly wrong and I don't know how it
was calculated.

Howard Stone
Map Cataloger, Brown University


On Tue, Jun 13, 2017 at 11:52 AM, <[log in to unmask]> wrote:

> Hello all,
> I am a rare materials cataloger who occasionally does maps, and I
> struggle sometimes with determining scale. I am currently working on a
> 1868 map with a bar scale in English miles. I found a record that gives
> an
> approx. scale of 1:57,217, but I can't figure out how they came to that
> number. The bar scale measures approx 2.3 in, with 1 inch approx 2.25
> English miles. When I compare 1 mile against the NSI I get a scale
> somewhere
> between 140,000-145,000, so I have no idea where the number 57217 comes
> from. I will try to attach some pics of the bar scale. Any help would be
> appreciated.
> Thank you
> -Silvana
>
>