# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: The Sun does not stop for anyone
From: Gary LaPook
Date: 2016 Dec 31, 07:01 +0000
According to Wikipedia, there are only eight map projections that are conformal. I challenge anybody to draft a small area plotting sheet utilizing the Universal Plotting Sheet form using any conformal projection other than the Mercator. Give it a go, Frank? Anybody else?

Nobody has responded to my challenge of telling a Mercator small area plotting sheet utilizing a Universal Plotting Sheet form created using the graphical method from one created using Meridional Parts. Anybody think they can spot a one minute tick mark on the latitude scale that varies only three ten-thousandths of an inch (3/10,000) from the pre-printed tic marks on the UPS?

Stan K wrote:
"As far as longitude goes, the N.O. 973 sheet has "1º Long. = 4 inches" printed on it Measuring the middle degree of latitude (39º to 40º), I get about 5.125 inches, so I would expect one degree of longitude to be about 5.125" x cos(39.5º) = 3.955".  Allowing for printing tolerance and my measuring error, this seems right.  This is the closest thing I have to a true Mercator chart.  FWIW, it has "MERCATOR PROJECTION" printed on it."

So apparently the acceptable tolerance in the printing of his MERCATOR chart is 0.045 inches which is four-hundred-fifty  ten-thousandths of an inch, (450/10,000) which is 150 times larger than the discrepancy in drawing the one minute latitude tick marks using the graphical method for constructing a MERCATOR small area plotting sheet.

Frank, you have not told me how you could tell the two apart as I asked in a prior post. If a true Mercator plotting sheet is one made using Meridional Parts and if you can't tell one made with the graphic method from that true Mercator small area plotting sheet then they are the same, they are both True Mercator plotting sheets.

"If it walks like a duck and quacks like a duck, it's a duck."

Here are the eight conformal projections.

To: garylapook@pacbell.net
Sent: Friday, December 30, 2016 10:18 AM
Subject: [NavList] Re: The Sun does not stop for anyone

OK...if we are to call a universal plotting sheet a conformal projection rather than a Mercator projection, it feels to me like I am missing something.  As nearly as I can tell, "conformal projection" is a broad category that encompasses at least the:
· azimuthal stereographic projection
· Mercator projection
· Lambert's conformal conic projection
· Guyou's Conformal Projection
For those who object to calling a universal plotting sheet a Mercator projection, what TYPE of conformal projection is it?
I am beginning to wonder if the universal plotting sheet perhaps represents an "unnamed conformal projection, resembling a Mercator more than any other."
Bob

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