[R-sig-Geo] Plotting data with multiple symbols and colours

[Edzer J. Pebesma]

I would try the alternative,

bubble(Error,maxsize=1.5)
bubble(Error,maxsize=1.5, key.entries=-10:10)

Doing what you want with spplot, you're basically thrown back at xyplot 
with asp="iso"; look at how key is formed there; with

spplot(Error, pch = ifelse(Error$error < 0, 95, 3), key.space = "right", 
cuts = -10:10)

I get funny pch changes in the key. I think that spplot passes an 
optional key argument to xyplot.
--
Edzer

ONKELINX, Thierry wrote:
> Dear listeRs,
>
> We're trying to create a map with interpolation errors of some spatial
> data. The idea is to plot the errors at the location of the data, with a
> "+" or "-" symbol to indicate whether they are positive or negative and
> a colour ramp that indicates the magnitude of the error. For now, we
> managed to get a plot with the correct symbols. But the colour ramp only
> works for the positive errors. The code to generate this:
>
> library("sp")
> library("RColorBrewer")
> library("lattice")
> set.seed(1)
> Error <- SpatialPointsDataFrame(matrix(runif(1000), ncol = 2), data =
> data.frame(error = runif(500, -10, 10)))
> trellis.par.set(sp.theme(set = FALSE, regions = list(col = c(rainbow(50,
> start = 0, end = 4/6), rev(rainbow(50, start = 0, end = 4/6))))))
> spplot(Error[Error$error >= 0, ], zcol = "error", sp.layout =
> list("sp.points", Error[Error$error < 0, ], pch = 95), key.space =
> "right", cuts = seq(-10, 10, length = 21), pch = 3)
>
> The questions:
> 1. For do we set the colour ramp for the negative values?
> 2. Can we change the key so it displays only absolute values or "-" in
> front of the negative values?
>
> All help is welcome.
>
> Thierry
>
> ------------------------------------------------------------------------
> ----
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek / Reseach Institute for Nature
> and Forest
> Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
> methodology and quality assurance
> Gaverstraat 4
> 9500 Geraardsbergen
> Belgium
> tel. + 32 54/436 185
> Thierry.Onkelinx at inbo.be
> www.inbo.be 
>  
>
> Do not put your faith in what statistics say until you have carefully
> considered what they do not say.  ~William W. Watt
> A statistical analysis, properly conducted, is a delicate dissection of
> uncertainties, a surgery of suppositions. ~M.J.Moroney
>
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