[R] spdep::poly2nb problem

[Roger Bivand]

This message should have had a more informative subject, and, given its
specialist character, been sent to R-sig-geo, as is recommended on the
Spatial Task View. From initial trials, the file you are using includes far
too much boundary detail, and appears to have been assembled from disparate
state/county maps (Florida is added late, not in sequence). With a malformed
input map intended for display only, you shouldn't be surprised that the
topology is wrong. I'll investigate whether there is a code issue, but the
real problem is the choice of a very inappropriate input map of an object
size of 64Mb for 56 objects, where you do not need all of the coastal
detail.

Roger


Philip A. Viton wrote:
> 
> I downloaded a US states+territories shapefile from
> http://www.weather.gov/geodata/catalog/national/html/us-state.htm
> and unzipped it into my working directory.
> Then in R (version 12.2.0 for ms-win32):
> 
> library(rgdal) # Version: 0.6-28
> library(spdep) # Version: 0.5-24 (loads sp: Version: 0.9-72)
> 
> # read in the data
> states<-readOGR(".","s_01de10")
> summary(states)
> 
> # now create a neighbors list
> states_nb<-poly2nb(states)
> # create a 0/1 matrix of the neighbors
> nb_mat<-nb2mat(states_nb,style="B",zero.policy=TRUE)
> # add names
> nms<-as.character(states$NAMES)
> # set the matrix names
> dimnames(nb_mat)<-list(nms,nms)
> 
> # now see which states have no neighbors
> rowSums(nb_mat)	
> # it turns out that Florida	seems to have zero neighbors.
> 
> I then repeated it with
> states_nb<-poly2nb(states,useC=FALSE)
> 
> and this time -- the computation takes a lot longer, of course
> --- Florida has 2 neighbors (correctly: AL and GA).
> 
> 
> Can anyone tell me what's going wrong here?
> 
> 
> Thanks!
> 
> 
> ------------------------
> Philip A. Viton
> City Planning, Ohio State University
> 275 West Woodruff Avenue, Columbus OH 43210
> viton.1 at osu.edu
> 
> ______________________________________________
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
> 


-----
Roger Bivand
Economic Geography Section
Department of Economics
Norwegian School of Economics and Business Administration
Helleveien 30
N-5045 Bergen, Norway

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