On Tue, 11 May 2010, Barry Rowlingson wrote:
On Tue, May 11, 2010 at 9:10 PM, Peter Larson <pslars...@gmail.com> wrote:
Hello,
I have a shp file of polygons of US counties and want to generate an
adjacency matrix (neighbor matrix).
Is there an easy way to do this? It seems like it should be trivial.
poly2nb in the spdep package will produce a list of adjacencies, and
from that you can make a full adjacency matrix if you want, but it
will probably be very sparse.
However... polygons that look adjacent might be very very close and
not found as adjacent by poly2nb. I'm investigating this with some of
my data at the moment...
Use the snap= argument to poly2nb() set to a larger but still small value
than default in that case, say 10m for projected coordinates.
Barry, if you'd like to try SVN spdep from R-forge (and maybe also SVN
rgeos from R-forge), you'll find a number of speedups. Any feedback on
those would be very welcome.
Roger
Barry
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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.biv...@nhh.no
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