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| Subject: | GISList: SUM : Projection for a specific area |
| Date: |
11/09/2002 09:21:37 PM |
| From: |
GIS (IPS) |
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It seems that the answer is either Lambert or Albers. The main difference
being that Albers is more involved when determining the parallels (like
Dimitri pointed out). I also consulted the sites as recommended by Holly
and Dimitri, which also helped me get some clarity on the subject. I also
took a look at the ArcGIS accompanied books, which included the book on
projections.
Thanks to all who replied. I really appreciate the help and expertise
you've shared. Below are all the responses I got. I left out the response
from Joe Loon, because we are still discussing the problem.
ciao
Dean Carstens
AfriGIS Environmental Solutions
Knysna
South Africa
Tel: +27-44-3750221
Cell: +27-82-7410315
Fax: +27-44-3750132
www.afrigis.co.za
ipsgis@safcol.co.za or dean@afrigis.co.za
************************************************************
Hi- Check this site
http://geography.about.com/cs/cartography/
<http://geography.about.com/cs/cartography/>
Holly Glaser
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Dean-
You may want to check out state plane coordinates
used in the US or Canadian projections used for surveying where distance
and bearing are conserved. One of these is probably close to your latitude
and you can flip the latitude and change the central meridian to near your
locations. Another idea - what projection did the British use to map your
area?
**************************************************
Lambert is the way to go, in my opinion.
Adrian Clark
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Depends where the area is really - Lambert Cylindrical Equal Area is OK near
the Equator, but shape distortion is bad towards the poles. Or there are the
Lambert and Albers Equal Area Conic which again have problems near the
poles.
You could consider pseudocylinidrical projections like Eckert or
Winkel, or pseudoconic projections like Bonne, which has no distortion on
the
central parallel or central meridian, or Werner.
Nigel James
***************************************************
(I'm not an expert in cartographic projections or geodesy, but I remember
some of my initial courses).
----------------------------
The choice of the projection might also depend on the shape of the area,
whether it is square/round/compact or, on the contrary, very thin/elongated.
Pascal Boulerie
***************************************************
How about that? Two postings back to back asking about equal area
projections! To (mostly) repeat my answer to an adjacent thread...
I'd recommend the Lambert Azimuthal Equal Area (LAEA) projection centered on
the region of interest. As its name indicates, the LAEA is a true equal
area projection.
For a useful guide to choosing projections, see the relevant topics in the
online version of the Manifold 5.00 user manual at
http://exchange.manifold.net/manifold/manuals/5_userman/mfd50General_Project
ions_Concepts.htm
and
http://exchange.manifold.net/manifold/manuals/5_userman/mfd50Guide_to_Select
ing_Map_Projectio.htm
The above material includes some passages taken literally word for word from
"Map Projections Used by the U.S. Geological Survey," Geological Survey
Bulletin 1532, Second Edition, John P. Snyder, 1982, and also from "An Album
of Map Projections," U.S. Geological Survey Professional Paper 1453, by John
P. Snyder. These books are in print at USGS, are cheap, and should be in
the library of everyone working with projections. The first is a bit on the
mathematical side while the second one is more popular and has great
illustrations.
* * * * * * * * * * * * * *
So I asked him: "What about Albers?"
That, too, would be fine. It's very similar to the Lambert, which is a
limited form of the Albers. See
http://exchange.manifold.net/manifold/manuals/5_userman/mfd50Albers_Conical_
Equal_Area.htm
Like the Lambert it is used for countries that are east-west in extent. The
Albers requires two standard parallels, which enables it to be more fitted
to the subject region at the cost of requiring more thought of the operator.
I mentioned the Lambert because it requires slightly less thought. :-)
Cheers,
Dimitri
************************************************************
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