-------- Original Message --------
Subject: Re: question about determining scale
Date: Thu, 12 Dec 2013 17:48:10 +0000
From: Mark Jackson <[log in to unmask]>
To: Maps, Air Photo, GIS Forum - Map Librarianship <[log in to unmask]>


I’m no cataloger, but as a geographer I use maps heavily and have taught map use and aerial photo interpretation courses for years, etc. Every map and image etc. generally has an average scale, but will vary a bit around the map depending on projection, the material it is printed on, topography, etc.

You’re email didn’t come through with any images, so I’m not seeing what you are seeing, but looking at that I’d say that whatever map you are using is clearly meant to be a 1 inch (map) = 1 mile (Earth), or 1:63,360, which is what I’d be looking for in the catalog anyway.

The ruler I commonly use with imagery and maps is divided into 10ths and 100ths of an inch but will commonly use a loupe and go for the thousandths digit. That is more for imagery than maps where the width of the ink line can make a huge difference. In this case a scale bar representing 2000 yards would need to be 1.1363636 inches to equal 1 mile on the ground. So, if you kind of measure from the center of the ink lines on each end of the scale bar you could come down from 1.14 to 1.137 and you’d come up with 1”=1 mile or 1/63,360.

Hopefully that helps.

--
Dr. Mark Jackson
Research Librarian
Geography ∙ Geology ∙ Civil Engineering ∙ CM ∙ FPM ∙ IT
Brigham Young University
2420 HBLL ∙ Provo UT 84602
801.422.9753 ∙ [log in to unmask]


On Dec 12, 2013, at 5:52 AM, Angie Cope, American Geographical Society Library, UW Milwaukee <[log in to unmask]> wrote:


-------- Original Message --------
Subject: question about determining scale
Date: Tue, 10 Dec 2013 18:23:02 -0500
From: Manon Theroux <[log in to unmask]>
To: [log in to unmask]


For those of you familiar with the "Cartographic Materials" rules for cataloging maps, I have a question about determining a representative fraction using a bar scale. I've copied below example #2 from Appendix B (Guidelines to Determine Scale and Coordinates), B2B (Conversion from a graphic scale). I don't know if the formatting will come through or not, so you might have to check your copy of CM. When I try to replicate the math, my calculator gives me "63,1578947368" for the right hand side. Rounding that off would give me a representative fraction of 1:63,158. Can anyone explain why CM gives 1:63,157 as the RF? Is there a reason you would round down?

Also, I'm curious, how likely is it that a map cataloger would have a ruler that measures to the accuracy of 1.14 inches anyway?

Thanks in advance for any help you can provide,

Manon Theroux
Head of Technical Services
U.S. Senate Library

------------------------------

2 000 yards in units of the bar scale
measure 1.14 inches with a ruler.
1.14 inches (on map) represents 2 000 yards (Earth)
2 000 yards = 2 000 × 36 inches
The ratio is: 1.14:(2 000 × 36)

or
or
1:63 157