require(sp)
data(meuse)
coordinates(meuse) = ~x+y
wt.copper <- wt.centroid(meuse, 'copper', sp=TRUE)
wt.zinc <- wt.centroid(meuse, 'zinc', sp=TRUE)
plot(meuse, pch=20, cex=0.75, main='Weighted centroid(s)')
points(wt.copper, pch=19, col='red', cex=1.5)
points(wt.zinc, pch=19, col='blue', cex=1.5)
box()
legend('topleft', legend=c('all','copper', 'zinc'),
pch=c(20,19,19),col=c('black','red','blue'))
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