[R-sig-Geo] Overlaying spplots

[Friderike Oehler]

Dear R Users,

I am struggeling to plot the z-column-values of a SpatialPointsDataFrame over a
polygon shapefile map SpatialPolygonsDataFrame) representing country borders. I
would like to use spplot in order to keep the scales. I followed the path that I
found in the help archive (http://thread.gmane.org/gmane.comp.lang.r.geo/2063).
This works fine to superimpose my points over the countries, however it does not
allow the z-values of the points to be shown.

The ADD=TRUE option does not seem to work for spplot. (Right or wrong?)

I also tried with levelplots and panel-functions, without success (admittedly I
am not an expert using these functions.) Without success were also my tries
using "overlay".

Any help would be much appreciated.
Many thanks in advance,
Friderike

# This is the shapefile:
EA=readShapePoly('C:/data/grassdata/EastAfrica/EastAfricaAdmin0',
proj4string=CRS("+proj=longlat +datum=WGS84"), force_ring=TRUE)
names(EA)
 [1] "CAT"        "AREA"       "PERIMETER"  "G2006_2_"   "G2006_2_ID"
"ADM2_CODE"  "ADM0_CODE"  "ADM0_NAME"  "ADM1_NAME"  "ADM1_CODE"  "ADM2_NAME" 
[12] "LAST_UPDAT" "CONTINENT"  "REGION"   

# This shows the shapefile
spplot(EA, zcol='ADM0_CODE', scales=list(draw=TRUE), xlim=c(30,52),
ylim=c(-10,18), col.regions='transparent', colorkey=FALSE)

# This is the SpatialPointsDataFrame:
 str(notinv)
Formal class 'SpatialPointsDataFrame' [package "sp"] with 5 slots
  ..@ data       :'data.frame': 1209 obs. of  1 variable:
  .. ..$ FQ: int [1:1209] 2 2 4 1 1 1 2 1 1 3 ...
  ..@ coords.nrs : int [1:2] 1 2
  ..@ coords     : num [1:1209, 1:2] 35.5 36.5 37.5 35.5 36.5 37.5 38.5 40.5
36.5 37.5 ...
  .. ..- attr(*, "dimnames")=List of 2
  .. .. ..$ : NULL
  .. .. ..$ : chr [1:2] "LON" "LAT"
  ..@ bbox       : num [1:2, 1:2] -17.5 -3.5 92.5 38.5
  .. ..- attr(*, "dimnames")=List of 2
  .. .. ..$ : chr [1:2] "LON" "LAT"
  .. .. ..$ : chr [1:2] "min" "max"
  ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
  .. .. ..@ projargs: chr NA

 # And that's what it looks like:
spplot(notinv, zcol='FQ', cuts=seq(1,max(Knotinvfreq$FQ),5), xlim=c(30,52),
ylim=c(-10,18), key.space='bottom', scales=list(draw=TRUE),
col.regions=terrain.colors(64,alpha=1))