[R-sig-Geo] Map2Poly: Error message

[Graham Cookson]

Dear Roger (...and the list)

Thank you Roger for that useful insight. I have tried your suggestion and,
once again, encountered some error messages. I've played around with it a
little bit, but I'm getting nowhere.

Perhaps you will have come across this problem before.

I tried your routine so I typed:

library(foreign)
library(maptools)
library(spdep)
map<-readShapePoly("englandandwales.shp")

But I got the following error:

Error in if (rD < 0) hole <- TRUE : missing value where TRUE/FALSE needed

Following the various examples in the help file I then tried

map<-readShapePoly("englandandwales.shp", IDvar="LABEL")

But now get the following error:

Error in from [j]: to [j]: NA/NaN argument

Error in coordinates(coords): unable to find the argument 'obj' in selecting
a method for function 'coordinates'


I've got this feeling I'm just doing something really silly but can't work
it out. Any help welcome. It may help to know that all I want to do is
produce a proximity matrix of contiguous boundary neighbours from the
Shapefile for now.


Again, I'm using R2.2.0 on an Apple iBook G4. The shapefile is a merged file
of England and Wales ward boundaries downloaded from Edina.ac.uk and was
merged in ArcView. It contains some 8,500 polygons and is 250MB.

Thank you,
Graham


-- 
Graham Cookson
Centre for Environmental Policy
Imperial College London
4th Floor, RSM Building
Prince Consort Road
London  SW7 2BP

Tel: 020 7594 9313
Mob: 07968 061323
Email: graham.cookson at imperial.ac.uk




> From: Roger Bivand <Roger.Bivand at nhh.no>
> Reply-To: Roger.Bivand at nhh.no
> Date: Thu, 3 Aug 2006 19:00:36 +0200 (CEST)
> To: Graham Cookson <graham.cookson at imperial.ac.uk>
> Cc: r-sig-geo at stat.math.ethz.ch
> Subject: Re: [R-sig-Geo] Map2Poly: Error message
> 
> On Thu, 3 Aug 2006, Graham Cookson wrote:
> 
>> 
>> 
>> Dear List,
>> 
>> I hope you can help me with this problem.
>> 
>> I am attempting to form an adjacency matrix and I'm trying to get my
>> shapefile into R. However, I get error messages at the initial stages.
>> 
>> I used the following code:
>> library(maptools)
>> library(spdep)
>> map<-read.shape("englandandwales.shp")
>> polylist<-Map2poly(map)
>> 
>> The map object is created fine and it finds all 8490 polygons, but the
>> Map2poly command generates the following error message:
>> 
>> Error in if (res[[6]] > 0) return(as.integer(-1)) else return(as.integer(1))
>> 
>> I have searched the web and the R Help Archives but can't find examples of
>> this problem occurring before.
>> 
>> The shapefile I am using was  created in ArcView by merging the separate
>> Wales and England shapefiles available from UK Borders at Edina.ac.uk
>> 
>> I am using R2.2.0 on an Apple iBook G4 running Mac OS X 10.3.9
>> 
>> I hope that this isn't a really stupid question
> 
> No, a relevant question on the right list with lots of helpful details.
> The error is thrown in Map2poly -> .get.polylist -> .ringDirxy, where the
> two last functions are internal ones, and the last one, with the error, is
> trying to determine the ring direction.
> 
> This is implemented differently in the readShapePoly() function also in
> maptools, which imports a shapefile into a SpatialPolygonsDataFrame. From
> there, you just coerce to SpatialPolygons to run poly2nb() -
> poly2nb(as(SPDF, "SpatialPolygons")) should work. Could you please try
> that route first, and let us know if it works?
> 
> If you'd prefer not to use the SpatialPolygonsDataFrame class, then we'll
> need to debug the older code, and then access to your shapefile (or a
> subset displaying the same symptoms) will be needed just for testing. In
> any case the output of sessionInfo() and of traceback() immediately after
> the error, together with the full error message would be very useful.
> Setting quiet=FALSE in the Map2poly() call may also show that some
> polygons are getting their ring directions reversed.
> 
> Roger
> 
>> 
>> Thanks!
>> Graham
>> 
>> 
>> 
>> 
>> 
>> 
> 
> -- 
> 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
> 
>