[R-sig-Geo] The length of common boundaries

[Markus Neteler]

On Tue, Oct 11, 2005 at 03:50:05PM +0200, Roger Bivand wrote:
> On Tue, 11 Oct 2005, Yilin Liu wrote:
> 
> > Dear all,
> > 
> > Any way to get the length of common boundaries shared by neighbouring
> > counties in a map in R?
> > 
> 
> The short answer is no. The R polygon objects do not have topology. 
> 
> The longer answer is that if you have e00 or ArcInfo binary vector layers,
> then the polygons are built from lists of directed arcs, and the arcs have
> lengths. So if your input data are in this format, it is feasible but is 
> not implemented.
> 
> It looks as though the GRASS6 vector format also provides similar
> information. But topology is a GIS thing rather than an R thing, so no
> solution within R is available.
> 
> If you use GRASS, it would be possible to look at how this might be done
> (read a shapefile into GRASS, output an ASCII dump of the arcs, which
> polygons they separate, and how long they are, and do something with this,
> not losing trace of which polygon(s)  belong to which observation - this
> was where progress stopped the last time I looked). Arc lengths would be
> nice for cartograms too.
> 

In GRASS 6 you can use v.to.db [1] to generate this information (should be
the combination of the options 'sides' and 'length'.

Markus

[1] http://grass.itc.it/grass60/manuals/html60_user/v.to.db.html


-- 
Markus Neteler     <neteler itc it>       http://mpa.itc.it
ITC-irst -  Centro per la Ricerca Scientifica e Tecnologica
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