[R-sig-Geo] help in constructing spatial weight matrix

[Roger Bivand]

On Tue, 12 Jun 2012, Fabricio Vasselai wrote:

> Dear list,
>
> Given a following up to this question, I have myself a somewhat similar
> question to that of Alsulami.
> I have a shp of Finnish cities and would like to generate for them a weight
> matrix of neighborhood based on inverse distance (for further use in
> Moran's I calculus). Here is the code I've been thinking of:
>
>
>  UF.shp <- readShapePoly(myshpfile.shp, IDvar="OBJECTID")
>  UF.nb <- poly2nb(UF.shp, queen=TRUE)
>  dsts <- nbdists(UF.nb, coordinates(UF.shp))
>  idw <- lapply(dsts, function(x) 1/(x/1000))
>  UF.listw <- nb2listw(UF.nb, glist = idw, style="B", zero.policy=TRUE)
>
>
> But it does not work and I can't figure how to fully adapt the idea to the
> shp I have.
> Anyone please could give me any tips?

Always provide the error messages, the output of sessionInfo(), and 
demonstrate the problem in a reproducible way with built-in data sets. If 
myshpfile.shp is not a character string, then the call to readShapePoly() 
will fail - did you mean: "myshpfile.shp"?

Roger

>
> Best,
>
> FABRICIO
>
>
>
>
> 2012/4/3 Roger Bivand <Roger.Bivand at nhh.no>
>
>> On Tue, 3 Apr 2012, dwl Al_Sulami wrote:
>>
>>  Dear there
>>> I am trying to construct spatial weight matrix using inverse distance,
>>> which means that high weight is given to near observations and ,vies versa,
>>> where  w_ij=w_ji and w_ii=0, Since, I am a new R user, I've tried many
>>> functions in sp,spdep packages and I find some functions to find weight
>>> matrix by using nearest neighbours and by distance-based neighbours, but I
>>> want to use all observations as neighbours and based on the inverse
>>> distance, I can construct the weights.
>>> Before I write the code I'll give some information about my data, I have
>>> the coordinates of   51 states (US states) , thus latitude and longitude of
>>> each states and based on the distance between each state I will give a
>>> weight for states where the weight is the the inverse of the distance.
>>> obviously , the weight matrix are symmetric.
>>> Then I've tried the following code
>>> data(location)# data.frame with 2 col and 51 row
>>> loc.sp = SpatialPoints(cbind(location$**latitude,location$longitude))
>>> sy8<-knn2nb(knearneigh(loc.sp,**k=50)) # for each state all other states
>>> are considered as neighbour
>>> dsts<-nbdists(sy8, loc.sp)
>>> idw<-lapply(dsts, function(x) 1/(x))
>>> sy<-nb2listw(sy8, glist=idw, style="B")
>>> col.mat <- listw2mat(sy)
>>> after running this code, I got symmetric matrix (51* 51), where w_ii=0
>>> and w_ij=w_ji
>>> but I am not sure if this is true!!!
>>>
>>
>> What do you mean by true - correct? There is at least one problem, that
>> you are not ensuring that the distances are computed by Great Circle. More
>> or less reproducing your code (data(locations) must be wrong):
>>
>> library(maps)
>> sts <- map("state", fill=TRUE, plot=FALSE)
>> library(maptools)
>> IDs <- sapply(strsplit(sts$names, ":"), function(x) x[1])
>> SPl <- map2SpatialPolygons(sts, IDs=IDs,
>>  proj4string=CRS("+proj=longlat +datum=WGS84"))
>> crds <- SpatialPoints(coordinates(SPl)**,
>>  proj4string=CRS("+proj=longlat +datum=WGS84"))
>> is.projected(crds)
>> library(spdep)
>> nbs <- dnearneigh(crds, 0, 10000)
>> # either crds a SpatialPoints object !is.projected(), or use longlat=TRUE
>> nbs
>> dsts <- nbdists(nbs, crds)
>> # either crds a SpatialPoints object !is.projected(), or use longlat=TRUE
>> summary(unlist(dsts))
>> # in km
>> idw <- lapply(dsts, function(x) 1/(x))
>> sy <- nb2listw(nbs, glist=idw, style="B")
>> col.mat <- listw2mat(sy)
>> all.equal(col.mat, t(col.mat), check.attributes=FALSE)
>>
>> I think that your "distances" were planar measures in geographical
>> coordinates.
>>
>> Hope this helps,
>>
>> Roger
>>
>>
>>  any commands and helps are appreciated
>>> Regards,
>>> Alsulami
>>>
>>>
>>>
>>>        [[alternative HTML version deleted]]
>>>
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>>>
>>>
>> --
>> Roger Bivand
>> Department of Economics, NHH Norwegian School of Economics,
>> 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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>>
>

-- 
Roger Bivand
Department of Economics, NHH Norwegian School of Economics,
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