[R-sig-Geo] drawing order in spplot

[Duncan Golicher]

Many thanks to everyone involved in putting together the excelent sp 
package. I have just used for teaching a brief intro to applied geostats 
with gstat. Students found life much easier than a year ago when I had 
to try to explain a less structured approach to the data.
A simple question arose after the class. According to the spplot 
documentation "for grids and polygons sp.layout is drawn afterwards (so 
the item will not be overdrawn by the grid and/or polygon)".
So in this example we expected a DEM to be drawn first, then municipal 
boundaries.

 > class(municipios)
[1] "SpatialPolygonsDataFrame"
 > class(chisgrid)
[1] "SpatialPixelsDataFrame"

municips <- list("sp.polygons", municipios)
spplot(chisgrid["dem"],sp.layout=municips)

The municipal boundaries are drawn first then overdrawn by the DEM, 
which was not what we expected or wanted. I couldn't find how to avoid 
this, apart from the simple solution of ..

image(chisgrid,col=terrain.colors(20))
plot(municipios,add=T)

instead of spplot.The figures on  http://r-spatial.sourceforge.net all 
appear to have the grid drawn first. Is there a way to reverse this?

Duncan

-- 

Dr Duncan Golicher
Ecologia y Sistematica Terrestre
Conservación de la Biodiversidad
El Colegio de la Frontera Sur
San Cristobal de Las Casas, 
Chiapas, Mexico

Email: dgoliche at sclc.ecosur.mx 

Tel: 967 674 9000 ext 1310
Fax: 967 678 2322
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