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