[R-sig-Geo] two questions about spdep package

[Roger Bivand]

On Wed, 12 Apr 2006, zhijie zhang wrote:

> Dear friends,
>  I met two problems in spdep package and hope to get help.
> 
> 1. "*coords* :matrix of point coordinates " appeared in spdep package for
> several times,but i can't find how to generate it, could anybody tell me how
> to generate the argument "* coords*",
>  e.g. tri2nb(*coords*, row.names = NULL)

It is a two-column matrix of the coordinate points. 

> 
> 2.  In "write.nb.gal:Write a neighbours list as a GAL *lattice* file, may
> also use newer GeoDa header format" , it refered the definition of lattice
> data. Frankly speaking, i'm not very clear about the difference of grid data
> and lattice data. Anybody who have a clear understanding about them give me
> a brief
> 

The terminology is pretty mixed up, even in GIS. As Danlin suggested, a 
GIS book may help, and the description in Waller & Gotway (2004) Applied 
Spatial Statistics for Public Health Data, Chapter 3, is good too. You are 
probably right that the word "lattice" on the write.nb.gal help page is 
not well chosen, when in fact lattice should refer to a tesselation, 
regular or irregular. GeoDa documentation calls GAL format files spatial 
weights files, while they could also be called spatial neighbour files. I 
will try to find a better fording for the help page.

Roger

> 
> --
> Kind Regards
> 
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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.Bivand at nhh.no