--- 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 ---