# [Proj] Re: Graduated equidistant projections for convenient co-ordinate transformations

strebe at aol.com strebe at aol.com
Tue Jul 31 15:13:40 EDT 2007

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Mike,

I'd need to know a little more about what you mean by "data maps". Most maps whose primary purpose is to show spatial distributions are expected to be equal-area. Equal-area conflicts with equidistant.

In your example of "zones of vegetation", there are the grossly defined "tropical", "temperate", and "arctic" zones, where latitude is the primary consideration. In those cases, precise distances mean little and the map's depiction of parallels is thought to suffice. If you are referring to ground-cover maps of a continental or global scope, then I should think an equal-area representation would be paramount. If you are referring to large-scale ground-cover maps, then the precise purpose of the map would strongly influence the choice of projection.

In this last case, is the ease of determining the precise geographic coordinate of a point more important than accurate distances measured between any two points on the map? More important than precise directions anywhere on the map? More important than being able to overlay and compare against existing printed maps? More important than...? The first goal conflicts with any other specific goal. That's fine. Your thesis isn't really about which map projection to use; that question is settled by need. Your thesis is really about the need for easy conversion from map coordinates to geographic coordinates. I haven't got a good sense yet for why that need trumps the others.

Regards,
-- daan Strebe, who is decidedly not a professor.

-----Original Message-----
From: Michael Ossipoff <mikeo2106 at msn.com>
To: Strebe at aol.com; proj at lists.maptools.org
Sent: Tue, 31 Jul 2007 4:47 am
Subject: Re: [Proj] Graduated equidistant projections for convenient co-ordinate transformations

Prof. Strebe--?
?

You wrote:?
?

>Easily converting between map coordinates and spherical coordinates is one?

>reason to choose a projection. When a mapmaker decides that's the most
>important?

>reason, the mapmaker does just what you suggest. Generally the mapmaker?

>decides other factors are more important.?
?

I want to emphasize that I was only suggesting those equidistant projections
for data maps, whose purpose is to show where, for instance,  certain zones
of vegetation are.?
?

Mike Ossipoff?
?

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