R help - Sep 2010 - Colorramp in Maptools, how to choose min and max values for the fg= argument

Hello,

I am using maptools for plooting geographical data.
The colour of the region indicates some region dependent value 
(population for example).

I pass the colours of the regions to the plot.Map function by defining 
the foreground colour:

jet.colors = colorRampPalette(c("#00007F", "blue",
"#007FFF",  "cyan",
"#7FFF7F", "yellow", "#FF7F00", "red",
"#7F0000"))
n=100
cols <- jet.colors(n)
Intervalls =  cut(as.numeric(Vector),n, na.rm=TRUE)
fgs <-cols[Intervalls] ## is there some option/possibility here to 
choose colours differently ??
plot.Map(Shape.map, fg=fgs, ol=NA, bty="n", xlab="",
ylab="", xaxt="n",
yaxt="n")

My problem is the following: I would like to choose minimal and maximal 
value of the colour palette, different from the minimal and maximal 
values of the Vector. For example: Vector=c(2,3,4,5,6), but the maximal 
colour should correspond to 10 and the minimal to 0.

I know, that maptools is not the most actual solution to plot maps, but 
I am building on an old code and therefore do not want to change it.

I would very much appreciate any help or hints!!
Katrin

Hi Katrin,


your problem is not related to maptools, rather to the base function
"colorRampPalette". In my opinion the easiest way to get what you want
is to use colorRamp:

Vector=c(2,3,4,5,6)
color.ramp <- colorRamp(c('white','black'))
map.colors <- color.ramp(Vector/10)

The 10 refers to the maximum value that you specified. You just have to adjust
the colors.


HTH
Jannis


--- schaber <kschaber at ipp.mpg.de> schrieb am Di, 21.9.2010:
> Von: schaber <kschaber at ipp.mpg.de>
> Betreff: [R] Colorramp in Maptools, how to choose min and max values for
the fg= argument
> An: r-help at r-project.org
> Datum: Dienstag, 21. September, 2010 15:42 Uhr
> 
> Hello,
> 
> I am using maptools for plooting geographical data.
> The colour of the region indicates some region dependent
> value (population for example).
> 
> I pass the colours of the regions to the plot.Map function
> by defining the foreground colour:
> 
> jet.colors = colorRampPalette(c("#00007F", "blue",
> "#007FFF",? "cyan", "#7FFF7F",
"yellow", "#FF7F00",
> "red", "#7F0000"))
> n=100
> cols <- jet.colors(n)
> Intervalls =? cut(as.numeric(Vector),n, na.rm=TRUE)
> fgs <-cols[Intervalls] ## is there some
> option/possibility here to choose colours differently ??
> plot.Map(Shape.map, fg=fgs, ol=NA, bty="n", xlab="",
> ylab="", xaxt="n", yaxt="n")
> 
> My problem is the following: I would like to choose minimal
> and maximal value of the colour palette, different from the
> minimal and maximal values of the Vector. For example:
> Vector=c(2,3,4,5,6), but the maximal colour should
> correspond to 10 and the minimal to 0.
> 
> I know, that maptools is not the most actual solution to
> plot maps, but I am building on an old code and therefore do
> not want to change it.
> 
> I would very much appreciate any help or hints!!
> Katrin
> 
> 
> -----Integrierter Anhang folgt-----
> 
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