How to check a large neighbourhood matrix?

Oscar:

If you produced the nb list in R, you can always summarize the nb list
to see whether there are units that don't have neighbors.

For instance:
#loading spdep
library(spdep)

#you have read a shapefile of postal code areas:

post<-read.shape("../yourshapefile.shp")

#since it is a polygon shapefile, a Map2poly and poly2nb function shall
do the trick (Roger will have better ideas than my naive ones)

post.nb<-poly2nb(Map2poly(post))
I think that Oscar had got this far using the prefered sp object:

SPDF <- readShapePoly()

nb <- poly2nb(SPDF)

but had needed to use the snap= argument to poly2nb() to overcome slivers 
in his polygons.
#then you summarize the nb list:

summary(post.nb)

This helps, because it says which have no neighbours. It will indicate how 
to "zoom" in on the plot for the locations of the polygons. To actually 
"zoom", use xlim= and ylim= in the plot method for nb objects.

If you want real control, consider writeOGR(SPDF, ..., driver="KML") in 
the rgdal package, and equivalently writeOGR() of the 
SpatialLinesDataFrame output by nb2lines(), and zoom to your satisfaction 
in GE using KML files.

Roger
The summary command will give you the characteristics of the neighbor
list object, including Number of regions, Number of nonzero links,
Percentage nonzero weights, Average number of links, regions that have
no links (which shall give you the idea whether or not some postal code
areas are connected) and the most and least connected regions

Hope this helps.

Regards,
Dr. Danlin Yu

Oscar Breugelmans wrote:
Dear all,

I am working on a neighbourhood matrix of the postal code areas in the
Netherlands. Reading the shapefile and producing the matrix is no problem
(after some help from Roger), but I am not completely confident that all
neighbours are recognized because there are a few polygon boundaries that
are topologically unclean. I have checked the shapefile as closely as
possible, but with 4000 postal code areas this is a hell of a job.
Plotting the matrix in R (using plot.nb) is also not an option because with
so many areas the individual connections are no longer visible. Thus, I
would like to zoom in on parts of the graph to check whether all neighbours
are defined correctly. I searched the web for methods to zoom in and out of
a graph in R, but couldn't find anything.
Does anyone know if there are ways to do this?

Oscar
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Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
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e-mail: Roger.Bivand at nhh.no

How to check a large neighbourhood matrix?

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