Map colouring via classInt and colour Brewer

On Wed, 5 Mar 2014, Alessandra Carioli wrote:

Dear all,

I have been trying to colour my maps using the same variable at different 
points in time employing the classInt and the RColorBrewer palettes. 
Although the matching between the map areas and data file is correct (I 
have checked), the colouring is wrong every time. I am sure the error is 
quite silly but I can?t understand where it lies? I have tried using a 
custom made palette or fixed breaks, but the colouring just does not work 
the right way! Any help on the matter would be greatly appreciated!

Ale

Library(classInt)
#number of class intervals
nclassint <- 7
# variable to be plotted
varofint <- varT1
length(varofint)

#define class intervals
cat3 <- classIntervals(varofint, nclassint,style = "jenks")
categ <- cat3
colpal   = brewer.pal(nclassint,"RdBu")
length(rev(colpal))

# Code for map: I want the reverse of the palette, from blue to red
colors <- findColours(categ,rev(colpal))
bins <- categ$brks
lb <- length(bins)

plot(shapefile, col=rev(colpal),axes=F)
length(varofint) == length(rev(colpal)) # FALSE, so rev(colpal) will be 
recycled,

plot(shapefile, col=rep(rev(colpal), length.out=100),axes=F)
This should be:

plot(shapefile, col=rep(rev(colpal), length.out=length(varofint)), ...

I was using North Carolina to replicate with - I wanted to demonstrate the 
consequences of unintended recycling in a reproducible way. The top of the 
code was:

library(maptools)
shapefile <- readShapeSpatial(system.file("shapes/sids.shp",
  package="maptools")[1], IDvar="FIPSNO",
  proj4string=CRS("+proj=longlat +ellps=clrk66"))
varofint <- shapefile$BIR74
library(classInt)
nclassint <- 7
cat3 <- classIntervals(varofint, nclassint, style = "jenks")
categ <- cat3
library(RColorBrewer)
colpal   = brewer.pal(nclassint, "RdBu")
colors <- findColours(categ, rev(colpal))
opar <- par(mfrow=c(2,1))
plot(shapefile, col=rev(colpal), axes=FALSE)
plot(shapefile, col=rep(rev(colpal), length.out=length(varofint)),
  axes=FALSE)
par(opar)

but the intention was:

plot(shapefile, col=colors, axes=FALSE)

Roger
when what you want is:

plot(shapefile, col=colors, axes=F)

Because recycling may be desired, it doesn't generate a warning.

Roger

title("Total Fertility Rate 1981", cex=1)
legend(1096133,4844461,fill=rev(colpal),legend=paste(round(bins[-length(bins)],2)
                                       ,"-",round(bins[-1],2)),cex=0.6, 
bg="white")

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Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no

Map colouring via classInt and colour Brewer

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