[Proj] RE: Proj Digest, Vol 50, Issue 22

[Gerald I. Evenden]

A few points:

1. anyone is ill advised to make distance measurements from small scale maps.  
If the maps cover global regions.  Distance measurement from small scale maps 
is absurd with any projection other than azimuthal equidistant which *only* 
gives distance from the origin of the projection.

2. For large scale maps, approximate distance can be determined with care and 
knowledge of the particular projection and scale.  Using distances determined 
from a map is *very* dependent upon the skill of the user and his/her correct 
resolution of the accuracy of the map derived values and the accuracy needs 
of the application.

3. Anyone seriously interested in determining distance will use a geodesic 
computation program.  For an excellent FORTRAN procedure and executable DOS 
program see:

http://www.ngs.noaa.gov/TOOLS/Inv_Fwd/Inv_Fwd.html

I second Mugnier's suggestion regarding Snyder's book and would add "How to 
lie with Maps" by Monmonier as a good read.

Can we drop this spam about tweeking obscure projections to do impossible 
jobs.

-- 
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