data(ncshp)
nc1 <- as.SpatialRings.Shapes(nc.shp$Shapes, as.character(nc.shp$att.data$FIPS))
df <- nc.shp$att.data
rownames(df) <- as.character(nc.shp$att.data$FIPS)
identical(rownames(df), getSRSringsIDSlots(nc1))
ncSRDF <- SpatialRingsDataFrame(nc1, df)
names(as(ncSRDF, "data.frame"))
rrt <- as(ncSRDF, "data.frame")$SID74/as(ncSRDF, "data.frame")$BIR74
brks <- quantile(rrt, seq(0,1,1/7))
cols <- grey((length(brks):2)/length(brks))
dens <- (2:length(brks))*3
plot.SpatialRings(ncSRDF, col=cols[findInterval(rrt, brks, all.inside=TRUE)])
plot.SpatialRings(ncSRDF, density=dens[findInterval(rrt, brks, all.inside=TRUE)])
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