test of spatial dependence?? - comp.soft-sys.sas

hello SAS-friends, I am a R beginner and try to ask a basic question: 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. PS, could someone confirm that "spatial dependence" is equivalent to "spatial correlation" or "spatial autocorrelation" or not. Thank you very much. XY -- say hello to friends of STAT and GIS

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 _________________________________________________________________ Talk now to your Hotmail contacts with Windows Live Messenger. http://clk.atdmt.com/MSN/go/msnnkwme0020000001msn/direct/01/?href=http://get.live.com/messenger/overview

Thanks for reply, David. No, I don't have the coordiates or the distance. In other words, my data are not point data. But I think there is a way to test of spatial dependence for areal data or lattice data. In this case, the variable of interest is typically the average value of an area instead of a point. Is a proximity matrix composed of 0 and 1 enough (1 means two units are adjacent and 0 not)? Do you how to do this? Thank you. Xu On 12/6/06, David L Cassell <davidlcassell@msn.com> wrote: > 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 > > _________________________________________________________________ > Talk now to your Hotmail contacts with Windows Live Messenger. > http://clk.atdmt.com/MSN/go/msnnkwme0020000001msn/direct/01/?href=http://get.live.com/messenger/overview > -- say hello to friends of STAT and GIS

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 _________________________________________________________________ Talk now to your Hotmail contacts with Windows Live Messenger. http://clk.atdmt.com/MSN/go/msnnkwme0020000001msn/direct/01/?href=http:/ /get.live.com/messenger/overview