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Map colouring via classInt and colour Brewer

3 messages · Alessandra Carioli, Roger Bivand

Original
Alessandra Carioli
# 
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
#define class intervals
cat3 <- classIntervals(varofint, nclassint,style = "jenks")
categ <- cat3
colpal   = brewer.pal(nclassint,"RdBu")
# 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)
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")
Roger Bivand
#
On Wed, 5 Mar 2014, Alessandra Carioli wrote:

            

      
      
      
    

        
length(varofint)

            

      
      
      
    

        
length(rev(colpal))

            

      
      
      
    

        
length(varofint) == length(rev(colpal)) # FALSE, so rev(colpal) will be 
recycled,

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

when what you want is:

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

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

Roger

            

      
      
      
    

        

      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Roger Bivand
    

    

      
      #
    

  


  

      
On Wed, 5 Mar 2014, Roger Bivand wrote:

        

            

      
      
      
    

        
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