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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | RE: GISList: Projections |
| Date: |
11/09/2002 09:21:36 PM |
| From: |
Dimitri Rotow |
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> I am trying to determine the proper projection to use. I am working with
> sea turtle satellite data. We have four turtles that are stationary at
> the moment off of the coast of Virginia and Delaware. What I am going to
> do is analyze and compare the sizes (area) of their home ranges using
> the Animal Movement Extension.
>
> So, this is a large scale map covering a small area on the globe and I
> want minimal distortion in area so that my home range comparisons are
> accurate. I am attempting to use UTM83 projection Zone 18, GRS80
> spheroid, map units: meters, distance units: kilometers.
>
> Does anyone foresee a problem with this or do they recommend anything
> else?
>
UTM is not an equal area projection, so it is a poor choice for this
application. If your study area covers more than 4 degrees of longitude it
is an especially poor choice due to the scale errors in UTM outside that
range (UTM is the ellipsoidal form of the original spherical Transverse
Mercator).
Depending on the size and shape of your region of interest, 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.
Cheers,
Dimitri
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