[R-sig-Geo] Good projection for N/S America?

Fri Apr 6 18:39:12 CEST 2007

Thanks, Roger.  There was a request to see the R code for these figures.
Attached is the script for the second PDF file plus the input boundary
file I used for the hemisphere.  The three projection functions are for
simple spherical, rather than ellipsoidal, models of the earth.  The
graticule generating function could be more elegant.  I'm not yet up to
speed with sp and the many new spatial capabilities in R so please
excuse the old style "lines()" format encoding and graphics.

Tim, I don't know whether proj4 could do the interrupted sinusoidal.

(See attached file: whemi.projs.r)(See attached file: whemi.lin)

r-sig-geo-bounces at stat.math.ethz.ch wrote on 2007-04-06 04:51:53:

> Since this topic is of general interest, I've made an exception and
> allowed (this once!) a posting of more than 200K. In general, if
graphics
> are big, please consider either an alternative device (png is often
OK),
> or posting just a URL to the real file.
>
> With apologies to list members on dial-up connections in the field,
>
> Roger
>
>
> On Thu, 5 Apr 2007 White.Denis at epamail.epa.gov wrote:
>
> > Yes, for many uses that is my choice also.  For the conterminous US
for
> > example, the Lambert azimuthal has lower mean distortion than the
> > commonly used standard projection, the Albers conical equal area,
> > although Albers was chosen by USGS as a standard because of lower
> > extreme distortion than many other possible projections.
> >
> > For our hemispherical application, because we were gridding the
data, we
> > wanted parallels of latitude to be parallel in the projected
coordinate
> > space, which we wouldn't get with the Lambert azimuthal.
> >
> > (See attached file: whemi.projs.pdf)
> >
> > Tim Keitt <tkeitt at gmail.com> wrote on 2007-04-05 10:56:09:
> >
> > > Thanks. My application is not that demanding. Really, I just want
it
> > > to look reasonable. My plan is to lay out the postings in the
> > > projected coordinates and then back transform into geographic
> > > coordinates for analysis. I tried lots of projections and found
> > > Lamberts Azimuthal Equal Area to be quite good. I like the look of
the
> > > Azimuthal Equidistant better, but figured equal area was a good
> > > choice.
> > >
> > > THK
> > >
> > > On 4/4/07, White.Denis at epamail.epa.gov
<White.Denis at epamail.epa.gov>
> > wrote:
> > > > Tim,
> > > >
> > > > It depends on which kind of distortion is of most concern.  For
many
> > > > types of extensive data, especially counts, for example, the
equal
> > area
> > > > property is desirable.  We used the Lambert cylindrical equal
area
> > > > projection with standard parallels of +/- 30 degrees for some
> > western
> > > > hemispherical work, see reference below.  (The center longitude
> > could be
> > > > -80 west, but that is less important than the choice of
parallels.)
> > > >
> > > > Before falling back on the Lambert as an easy to use projection,
I
> > tried
> > > > to get several ESRI products to implement an interrupted
projection
> > > > using the sinusoidal projection, in part for reasons given in
the
> > second
> > > > reference.  I used a separate center longitude for north and
south
> > of
> > > > the equator and the appearance is certainly more satisfactory
than
> > the
> > > > Lambert in my opinion.  I'll attach a PDF of an illustration of
this
> > > > approach generated in R that I hope you will get but not the
rest of
> > the
> > > > list unfortunately.  I can send PDFs of the references also if
> > needed.
> > > >
> > > > Denis
> > > >
> > > > Lawler JJ, White D, Neilson RP, Blaustein AR.  2006.  Predicting
> > > > climate-induced range shifts: model differences and model
> > reliability.
> > > > Global Change Biology 12:1568-1584.
> > > >
> > > > White D.  2006.  Display of pixel loss and replication in
> > reprojecting
> > > > raster data from the sinusoidal projection.  Geocarto
International
> > > > 21(2):19-22.
> > > >
> > > > (See attached file: whemi.sinus.pdf)
> > > >
> > > > r-sig-geo-bounces at stat.math.ethz.ch wrote on 2007-04-04
12:17:39:
> > > >
> > > > > Anyone know of a particularly good map projection for showing
all
> > of
> > > > > North and South America without too much distortion?
> > > > >
> > > > > THK
> > > > >
> > > > > --
> > > > > Timothy H. Keitt, University of Texas at Austin
> > > > > Contact info and schedule at http://www.keittlab.org/tkeitt/
> > > > > Reprints at http://www.keittlab.org/tkeitt/papers/
> > > > > ODF attachment? See http://www.openoffice.org/
> > > > >
> > > > > _______________________________________________
> > > > > R-sig-Geo mailing list
> > > > > R-sig-Geo at stat.math.ethz.ch
> > > > > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> > > >
> > >
> > >
> > > --
> > > Timothy H. Keitt, University of Texas at Austin
> > > Contact info and schedule at http://www.keittlab.org/tkeitt/
> > > Reprints at http://www.keittlab.org/tkeitt/papers/
> > > ODF attachment? See http://www.openoffice.org/
>
> --
> Roger Bivand
> Economic Geography Section, Department of Economics, Norwegian School
of
> Economics and Business Administration, Helleveien 30, N-5045 Bergen,
> Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
> e-mail: Roger.Bivand at nhh.no
>
> _______________________________________________
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