dot-density-map.R

# Dot density map
# Eventually should be like http://www.radicalcartography.net/index.html?frenchkisses

library(maptools)

nc_SP <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1],
 proj4string=CRS("+proj=longlat  +ellps=clrk66"))
 
## Not run:
pls <- slot(nc_SP, "polygons")
pls_new <- lapply(pls, checkPolygonsHoles)
nc_SP <- SpatialPolygonsDataFrame(SpatialPolygons(pls_new,
 proj4string=CRS(proj4string(nc_SP))), data=as(nc_SP, "data.frame"))
## End(Not run)
 
col1 <- dotsInPolys(nc_SP, as.integer(nc_SP$SID74))
col2 <- dotsInPolys(nc_SP, as.integer(nc_SP$SID74/2))

pt_size = 0.5

plot(nc_SP, axes=TRUE)
points(col1, pch=19, col="red", cex = pt_size)
points(col2, pch=19, col="blue", cex = pt_size)