Trust the bar scale only because it was designed to represent the nominal
scale of the map. If a world map, then the scale is true at the equator.
Your method of measuring at random points is not a good idea unless the map
projection is equidistant--and only works along the central meridian and
equator.

On Fri, May 18, 2018 at 11:55 AM, Rick Grapes <[log in to unmask]> wrote:

> Hi all,
>
>
>
> I have a calculating scale question.  This map I’m cataloging has a bar
> scale.  I measured the bar, did the math, and got the ratio.
>
>
>
> Just for the fun of it I also measured between 2 points on the map, as far
> apart as the map would allow, obviously much greater than the bar scale,
> then measured between the same 2 points on google maps, and again did the
> math.  The difference was about 10%.  Which calculation would you trust?
> Granted, either entries in the 255 would be an approximation.  A potential
> issue could be divergent projections etc.  Any suggestions?
>
>
>
> Rick Grapes
>
> BYU Map Cataloger
>



-- 
Maureen Kelley, PhD
Lecturer, Geography & Global Studies Department
San Jose State University