[R-sig-Geo] create listw-objects from shapefiles

[Roger Bivand]

On Mon, 4 Dec 2006, Catherine Linard wrote:

> Dear R-sig-geo list,
> 
> I would like to do some spatial analyses such as 
> moran.test, for which I need a listw. I have 
> shapefile data, so I tried to apply the following steps:
> 
> -         create spatial polygons with readShapePoly (maptools package)
> -         create neighbours list by poly2nb (spdep package)
> -         create spatial weights with nb2listw
> 
> I get an error message for the last step saying 
> that my nb-object is empty but I have results in 
> the neigbours list object in the previous step


No, you have two observations with empty sets of neighbours:

> 2 regions with no links:
> 44 78

Either fix that - for example with edit.nb(), or accept that this is 
reasonable - they really have no neighbours, and set zero.policy=TRUE.

Roger


> Here are my results:
> 
>  > lyme <- readShapePoly ("Filename", 
> proj4string=CRS(as.character (NA)), verbose=FALSE)
> 
>  > summary(lyme)
> Object of class SpatialPolygonsDataFrame
> Coordinates:
>          min      max
> r1 22120.69 295156.8
> r2 21153.22 244018.8
> Is projected: NA
> proj4string : [NA]
> Data attributes: different attributes

> 
>  > lyme_nb <- poly2nb(as(lyme, "SpatialPolygons"))
>  > summary(lyme_nb)
> Neighbour list object:
> Number of regions: 589
> Number of nonzero links: 3314
> Percentage nonzero weights: 0.9552607
> Average number of links: 5.626486
> 2 regions with no links:
> 44 78
> Link number distribution:
> 
>    0   1   2   3   4   5   6   7   8   9  10  11  12  14  15
>    2   2  10  35  75 170 144  86  38  17   5   1   2   1   1
> 2 least connected regions:
> 8 363 with 1 link
> 1 most connected region:
> 73 with 15 links
> 
>  > lyme_w <- nb2listw(lyme_nb,glist=NULL,style="W",zero.policy=FALSE)
> Error in nb2listw(lyme_nb, glist = NULL, style = "W", zero.policy = FALSE) :
>          Empty neighbour sets found
> 
> Is there something wrong? Do I miss something? 
> Thank you very much for any help!
> 
> Catherine
> 
> Catherine Linard
> University of Louvain
> Department of Geography
> Place Pasteur, 3
> B - 1348 Louvain-la-Neuve
> BELGIUM
> 
> Tel: +32/10/47.28.67
> Fax: +32/10/47.28.77
> e-mail: linard at geog.ucl.ac.be
> 
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> 

-- 
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