projection questions

[Jeff Portwine]

Well, I guess I didn't mean specifically "New England" but the general
area.... my map includes most of Pennsylvania, New Jersey, Massachusetts,
Conneticut, Vermont, Rhode Island, New York, and part of Maine.

It is entirely possible that as you said i'm being misled by the Map Point
map... and that I just have to get used to how this looks , but regardless I
need to understand what's going on so that when the people I'm doing this
for ask me I can explain the difference :)

I put up a quick and dirty web page:   http://www.aiedail.net/maps  so that
you can see exactly what I'm talking about (I didn't want to attach images
to an email for the entire list).    I hope that these images will
demonstrate what i've been trying to write in text.

I'm not actually using mappoint data to create the map, so I have no idea
how they project the data when they generate maps...  but I can't really
seem to make my output look any different regardless of what I use for
output projection.

If there is no way to make it look the same that's probably OK, i'm just
trying to understand what's happening.

Thanks for the time, hope  the picture posting helps.

-Jeff


> ----- Original Message -----
> From: "Ed McNierney" <ed at TOPOZONE.COM>
> To: <MAPSERVER-USERS at LISTS.UMN.EDU>
> Sent: Monday, January 24, 2005 2:33 PM
> Subject: Re: [UMN_MAPSERVER-USERS] projection questions
>
>
> Jeff -
>
> You're confusing this New Englander with your definition of "New England"
> <g>.  It doesn't include Pennsylvania, Pennsylvania doesn't have much of a
> coast, and the coast from New York City to Eastport, Maine runs 4.2
> degrees north and 7.0 degrees east, which is quite a bit closer to east
> than north, particularly in a lat/lon projection!
>
> I think you're being misled by your MapPoint map.  I'm going to guess that
> it uses something like an Albers projection centered on the continent.
> This will cause the eastern portions of the US to appear to rotate
> counterclockwise.
>
> As a simple check, the northern borders of Pennsylvania, Connecticut,
> Rhode Island, and Massachusetts are all generally straight lines running
> east-west at constant latitude.  Are they running straight right to left
> on your Map Point map, or are they running at an angle?
>
> Stretching the extents will not reproject the image.  If your MapPoint map
> doesn't have the Connecticut-Massachusetts border as a right-left line, no
> amount of X and Y stretching will rotate it into the place you expect.
>
> If you want to duplicate the MapPoint map, the first thing you need to do
> is find out what projection it uses.  It sounds like it is NOT the
> projection you think it is, and I don't think it's very productive to try
> to guess at it.
>
>     - Ed
>
> P.S. Please remember to always send replies to the whole list - thanks!
>
> Ed McNierney
> TopoZone.com
>
>