[Proj] Re: Comments of tmerc, etmerc and ftmerc errors

Gerald I. Evenden geraldi.evenden at gmail.com
Sat Jun 14 22:08:17 EDT 2008

On Saturday 14 June 2008 8:32 pm, strebe wrote:
> On Jun 14, 2008, at 8:08:47 AM, "Gerald I. Evenden"
> <geraldi.evenden at gmail.com> wrote: This is the place where we will
> apparently never agree. I would never use small scale maps for
> distance/azimuth measurements and anyone who does is ill advised.
> You know, Mr. Evenden, you are the one who touted the superiority of 
equal-area maps for such purposes (quoting from your previous e-mail):
> >Extended geographic range usage of any conformal projection is a
> > contentious  issue as any resultant grid system has sufficiently large
> > scale errors as to make the Cartesian usage of the grid very
> > questionable.
> >
> >Your comment:
> >>This is true of any projection. It is true that conformal projections
> >> carry an inevitable disproportion of areas, but that's not related to
> >> scale error.
> >
> >My sentense had nothing to do with area and by Cartesian usage I was
> > denoting  measuring distances, azumuths, etc. from the Cartesian data and
> > it certainly seems that scale error greatly affects these measurements.
> You're not arguing with me. I did not bring up using maps for arbitrary
> distance/azimuth measurements. You did, and you did so in order to prove
> the superiority of equal-area projections over conformal projections for
> small-scale usage. So now you are arguing with yourself. This is a matter
> of public record. So is the rest of your weaseling over the course of this
> discussion.
> As far as your tirade below goes, I dare you to find anyone who thinks we
> should use maps when something else is better. I dare you to find someone
> who thinks most thematic mapping should be on anything other than
> equal-area maps. Those are straw men. Meanwhile, because you apparently
> can't imagine any use for small-scale maps that is not tied to area
> mensuration or estimation, you call for the elimination of conformal maps.
> You might ponder that it's dogma and your own limited imagination that lead
> you to such conclusions, not logic, and not real-world needs.
> Regards,
> -- daan Strebe

My, my, my.  Our mutual respect overfloweth again.

My original comments, way back when, were in the response to the general 
subject on the use of TM for wide longitude mapping---even to global extent.  
In response to this general subject I voiced my feelings about the use of 
conformal maps for small scale mapping.  A simple and calm soapbox expression 
of opinion.

To be sure there are occasional exceptions and non-equal-area maps are called 
for.  I can even think of a good example that I seem to remember from Synder 
and Voxland's book where a global map was constructed for the Muslim 
community that allowed easy determination of the azimuth from anywhere on the 
globe to Mecca.  And there are certainly other examples but I would bet that 
for a high percentage of application the equal area projection is the 
preferred choice.

As a final comment about your accusation of straw men, they certainly seem 
alive and well.  Why do we persist on seeing global Mercator maps.  Members 
of this email group want to use wide coverage TM.  As far as I can see, 
conformal mapping is a dinosaur.  GPS, modern surveying methods and small 
portable computing power has eliminated any need for it.  We don't use a 
sextant and chronometer any more.  I also feel there is a place for 
non-equal-area maps in special situations.

Looking back to my email that started our little feud, except for the 
subsequent, unfortunate sidetrack into scaling details, I have done nothing 
but simply expand on the theme of criticizing conformal projections in the 
original last paragraph.  I still do not understand how you came up with the 
original question with "equal area" as I can't find equal-area mentioned in 
the paragraph.  I think you were just baiting me for old time's sake. ;-)  Of 
course, I may have been baiting you with my paragraph.

Have a good weekend!

The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939)  British psychologist

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