[R-sig-Geo] Using neighbours outside the area of analysis for constructing spatial weight matrices

[Roger Bivand]

On Tue, 8 Feb 2011, alfonso echazarra wrote:

> Hello,
>
> I am constructing a spatial weight matrix and would like to use 
> neighbours that are not part ofthe area I am analysing. In this case, I 
> am investigating crime rates within Madrid and I would like to use 
> Madrid's adjacent census tracts to construct the spatial weights for 
> census tracts on the edge of Madrid (queen contiguity rule). Is that 
> possible? Spatial weights matrices and dataset that are analysed need to 
> be of same size?
>

With very few exceptions, they need to be of the same size. The exception 
is that localmoran.sad() and localmoran.exact() take a select= argument to 
select the zones to be tested, but even here the length of the nb object 
and the number of observations must agree - you just do not have to 
compute local Moran's I for all of the observations. My impression is that 
the distributional assumptions behind the tests would be affected if some 
of the x_j were omitted from computation but included in the spatial lags 
through w_{ij}. It may be possible to construct a lagged variable for 
inclusion in a regression, but I'm not sure whether this would address the 
edge effects you seem to be concerned about.

Roger

>
> Thanks,
> Alfonso Echazarra
>
>
>
>
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>
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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