Completion of two SpatialPolygonsDataFrames with spplot

Question

I have a bunch of data that I built at the county level without borders . I would like to add to state borders. I have a shapefile status file (polygons), but spplot does not seem to be able to add on top of the previous map. Is there a way to do this without rewriting the panel function to take two SPDFs (which seems pretty specialized for what is probably other people's problem)?

Here's a reproducible example:

 library(sp) Srs1 = Polygons(list(Polygon(cbind(c(2,4,4,1,2),c(2,3,5,4,2)))), "s1") Srs2 = Polygons(list(Polygon(cbind(c(5,4,2,5),c(2,3,2,2)))), "s2") county <- SpatialPolygonsDataFrame( SpatialPolygons(list(Srs1,Srs2)), data.frame( z=1:2, row.names=c("s1","s2") ) ) SrsA <- Polygons(list(Polygon(cbind(c(3,5,5,1,3),c(3,4,6,5,3)))),"sA") state <- SpatialPolygonsDataFrame( SpatialPolygons(list(SrsA)), data.frame( z=1,row.names="sA" )) spplot( county, zcol="z",col=NA ) spplot( state, add=TRUE ) # Note the add=TRUE does nothing here, but that the spirit of what I want to accomplish 

Answer 1

To override using the spplot function, you can use the sp.layout argument. For example, create lists of relevant layout elements, for example

 spCounty <- list("sp.polygons", county, col = NA) spState <- list("sp.polygons", state) 

Then write down by passing the above list items as a list to sp.layout :

 # spplot(county, zcol = "z", col = NA, sp.layout = list(spCounty, spState)) # actually, you only need to pass the second layout item to sp.layout spplot(county, zcol = "z", col = NA, sp.layout = spState) 

The x and y constraints may not be valid if the two spatial data frames do not overlap completely. You can fix this if necessary by extracting the appropriate limits from bbox(obj)

For example,

 theMin <- pmin(bbox(county)[,1], bbox(state)[,1]) theMax <- pmax(bbox(county)[,2], bbox(state)[,2]) spplot(county, zcol = "z", col = NA, sp.layout = spState, ylim = c(theMin[2], theMax[2]), xlim = c(theMin[1], theMax[1]))