Plotting data with multiple symbols and colours

-----Oorspronkelijk bericht-----
Van: Edzer J. Pebesma [mailto:e.pebesma at geo.uu.nl] 
Verzonden: woensdag 14 maart 2007 13:40
Aan: ONKELINX, Thierry
CC: r-sig-geo at stat.math.ethz.ch
Onderwerp: Re: [R-sig-Geo] Plotting data with multiple 
symbols and colours

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