On Wed, 25 Aug 2004, Jeff Hollister wrote:
Howdy All,
I am looking for some good tutorials (books, websites, whatever) for
calculating/testing for Spatial Autocorrelation using R.
Specifically, I am wanting to test for autocorrelation of a number of
variables measured at a set of discrete locations.
From your signature line, Environmental Data, spatial autocorrelation
could mean a number of things, depending on whether the variables could be
measurements of a continuous surface of values at your discrete locations,
or whether the discrete locations are spatial entities formed as areal
aggregations of some kind. Since you mention spdep below, I'm assuming
that the data you are working on refer to spatial entities, for which
Moran's I would be a reasonable choice of test. If the variable of
interest isn't of this form, then other packages are more relevant (see R
spatial projects link below).
Up to this point I have been exploring the spdep package and I can get
moran.test to work, but I am concerned that somewhere along the line I
may not be doing things correctly. Hence my request for a tutorial so
that I may brush up on my autocorrelation basics, specifically
autocorrelation with R, and reassure myself that the results I am
getting aren't bogus.
Admittedly, the help page for moran.test() simply refers to Cliff, A. D.,
Ord, J. K. 1981 Spatial processes, Pion, p. 21 as the original source, and
the sids vignette (see the foot of the output of help(package=spdep) to
locate it on your system) is incomplete. My guess is however that if your
data are for spatial entities, theb constructing a sensible
neighbour weights is at least 75% of the work - you will also see this in
Virgilio Gómez-Rubio's DCluster package, and the existing sids
vignette does cover that a little. Completing and improving this vignette
is on my TODO list.
If you are unsure of the result, and want to stay within the R framework,
consider calculating Moran's I using DCluster, or gearymoran() in ade4.
Beyond that, you could access the GeoDa software (Windows, not R) and
documentation at http://sal.agecon.uiuc.edu/csiss/geoda.html, the site
also housing the R spatial projects web pages:
http://agec221.agecon.uiuc.edu/csiss/Rgeo/
Please contact me off-list, or on the R-sig-geo list if you feel that
would help.
Best wishes,
Roger Bivand
Thanks in advance for any suggestions!
Jeff Hollister
*
Jeffrey William Hollister
Ph.D. Candidate
Environmental Data Center
Department of Natural Resources Science
University of Rhode Island
office: (401) 874 5054
fax: (401) 874 4561
cell: (401)556 4087
http://www.edc.uri.edu/personal/jeff/home/jwh_cv_full.htm
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--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: [EMAIL PROTECTED]
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