[R-sig-Geo] How to extract part of Map object using maptools

[Hisaji Ono]

Hi.

 Rmap can extract parts of Map object as follows.

 columbus<- shapefile("columbus.shp") " load shapefile

 plot(columbus[columbus$CRIME > mean(columbus$CRIME)]) # filter by attribute
& plot

 But I don't know how to do this by maptools.

 Regards.