--- Begin Forwarded Message ---
Date: Wed, 28 Feb 2001 14:52:51 -0600
From: "Dr. Dennis Fitzsimons" <[log in to unmask]>
Subject: (Fwd) Re: Fw: GIS in the News! <fwd>
Sender: "Dr. Dennis Fitzsimons" <[log in to unmask]>

Sorry... too many inaccuracies here to let this pass.

There is no reason to compare a Peters projection to a Mercator.  Peters is but
one of many "equal-area" projections (and not a particularly good one at that).
The Mercator projection is a mathematically derived (not a "developable"
cylindrical projection) and has the properties of "true shape" (really true
angles) or conformality and "true direction".  For navigation, it is most
valuable for showing a loxodrome or rhumb line... a line of constant compass
bearing... as a straight line.  Only when the loxodrome follows a meridian or
the Equator will the straight line represent the great circle route (shortest
distance).  A projection commonly used for great circle routes is the
Gnomonic.

Lecture over... go in peace.

D.Fitzsimons
Department of Geography
Southwest Texas State University
San Marcos, TX


> --- Begin Forwarded Message ---
> Date: Tue, 27 Feb 2001 17:48:31 -0500 (EST)
> From: Ken Grabach <[log in to unmask]>
> Subject: Re: Fw: GIS in the News! <fwd>
> Sender: Ken Grabach <[log in to unmask]>
>
>
> I will leave alone the notion that Peters' projection is an acceptable
> alternative to the Mercator projection. I respond to the parenthetical
> note that Mercator projection was 'actually' invented by Kremer.  Gerhard
> Kramer created a map world map using a cylindrical projection, which appeared
> in the first 'atlases', that is bound sets of maps.  His name appears on the
> map as Mercator, because that is the Latin form of his surname, which means
> merchant, as does Kramer in German and Netherlandish.  So the Mercator
> projection was invented by Kramer because they were the same guy!
>
> There has been discussion before about why the cylindrical projection was used
> on world maps.  This reason had nothing to do at the time with how land areas
> are portrayed.  It has to do with the fact that great circle routes, including
> meridians, appear as straight lines.  And the meridians also appear at right
> angles to the lines of latitude.  In other words, its graticule is a grid!
> (reference to discussion about latitude and longitude ;} .)   This fact makes
> a map on such a projection most useful indeed for navigational purposes, as
> the navigator can show her or his route as a straight line drawn with the
> straight edge, and can then report the bearings with a great deal of accuracy
> to the master on the bridge of the vessel.
>
>
> On Tue, 27 Feb 2001, Johnnie Sutherland wrote:
>
> > >
> > > Does the Mercator Projection commonly used for school and other mass
> > > consumption maps (but invented by Gerhard Kremer in the 16th Century as an
> > > aid to maritime navigation) give us a distorted view of our importance in
> > > the world?  Check it out at
> >
>
>
> ___________________________
> Ken Grabach                           <[log in to unmask]>
> Maps Librarian                         Phone: 513-529-1726
> Miami University Libraries
> Oxford, Ohio  45056  USA
> --- End Forwarded Message ---

Dr. Dennis Fitzsimons
Department of Geography
Southwest Texas State University
San Marcos, TX  78666-4616
512.245.3200
--- End Forwarded Message ---