[R-sig-Geo] delete region from shapefile / map only certain regions

[Roger Bivand]

On Sat, 5 Jan 2008, stefan lhachimi wrote:

> Hello,
> I have two qeustions about shape files:
>
> First, I have a shp.file for all counties in Germany. Funnily enough,
> two counties are just lakes for which
>    I do not have covariates. Is there a possibilty delete them, so
> they don't show on the map and do not affect my analysis.

If you use readShapePoly() in maptools, they will be read into a 
SpatialPolygonsDataFrame object. You subset it using "[" as other data 
frame objects - see the examples in ?readShapePoly, and more class 
documentation in the sp package. Create a logical vector to do the 
subsetting.

>
>
> Second, is it possible just to plot parts of the map, given some
> condition (say, part of a state or a larger region)?
>

Either subset in the same way (counties in a land, for example), or use 
the xlim= and ylim= arguments to the plot() or spplot() methods for the 
class, depending on what you need. For plot(), you need to set the class 
intervals for colour filling yourself, for spplot() you can set up a 
legend and class intervals automatically.

Hope this helps,

Roger

> I hope these question are not too trivial, but I couldn't find
> anything adequate in the mailing list.
> Happy new Year,
> Stefan
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at stat.math.ethz.ch
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>

-- 
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