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### Re: test of spatial dependence?? #3

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```I would recommend you read the monograph on spatial autocorrelation by
Daniel Griffith. It provides good explanations,examples and formulae so
you can code the appropriate solution for your problem in R or SAS or
whatever.

You don't necessarily need distance for spatial autocorrelation. What
you do need is data on the topology of your fields and then create some
type of adjacency matrix. The simplest is a binary matrix for adjacent
sides - if two fields share a common border, code 1, if they do not,
code 0.

For small problems, you can usually do this by hand, based on a map of
the area of interest. Larger problems usually require a suitable GIS
that can create such an adjacency matrix - ARCVIEW used to do this
specifically for calculating spatial statistics, but I am not sure it
still does. Once you have this matrix, the standard spatial correlations
are straightforward to code.

Hope this helps,

Frank

-----Original Message-----
From: David L Cassell [mailto:davidlcassell@MSN.COM]
Sent: Wednesday, December 06, 2006 12:46 AM
Subject: Re: test of spatial dependence??

sasncsu@GMAIL.COM wrote:
>
>hello SAS-friends,
>
>I am a R beginner and try to ask a basic question:

If you are an R beginner, are you asking in the right place?
R has lots of spatial statistics capabilities, and a good mailing list
too.

That said, I'll stick to SAS here.

>How to test the spatial dependence of a column of data? for example, I
>have
>25 agricultural fields, and I measure the average slope (%) or pH for
>each field. All I have is 25 numbers.

Do you have distances between fields, or {x,y} coordinates?
If you don't have some capability of constructing the distances, then
there's no way to know which fields are 'close' to each other and which
are far apart.  So there would be no way to do this determination.

>PS, could someone confirm that "spatial dependence" is equivalent to
>"spatial correlation" or "spatial autocorrelation" or not.

It depends on who asked the question.  Really.  'spatial dependence' is
a really vague term.  What are you planning on using the information
for?  Modeling spatial correlations in some manner of linear model?

>Thank you very much.
>XY
>
>
>--
>say hello to friends of STAT and GIS

Take a look at PROC VARIOGRAM to do the modeling of the spatial
structure.

HTH,
David
--
David L. Cassell
mathematical statistician
Design Pathways
3115 NW Norwood Pl.
Corvallis OR 97330

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Reply FIvis (31) 12/6/2006 7:07:01 PM

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