# [R] Color intervals in image.plot function

Jim Lemon jim at bitwrit.com.au
Tue Feb 9 01:06:34 CET 2010

```On 02/09/2010 04:45 AM, FMH wrote:
>
> Hi,
>
> The script below is my current coding in order to produce a contour plot of temperature across altitude and time. In my case, time,altitude and temperature are represented by x, y and z variables.
>
>
> ##############################################
> Brazilan.Pallete<- colorRampPalette(c("blue","green","yellow","red"))
> image.plot(x, y, z, col = Brazilan.Pallete(50))
> contour(x,y,z, levels = seq(1, 40, by = 1), add = TRUE, col = 'peru')
> ##############################################
>
>
>
> The plot worked fine but i found difficult to fix the interval of the color corresponding to z value. In my case, the range of z values is between 1 and 40 and  i'd like to fix the color in the image correspoding to four sub-intervals of z values. For instance:
>
> 1. 1<  z<  10 : blue
> 2. 11<  z<  20: green
> 3. 21<  z<  30: yellow
> 4. 31<  z<  40 : red.
>
> I did't find a suitable code to do this. Could someone please give an advice on this matter?
>
Hi Fir,
The above is saying to me that you want to do this:

zcol<-c("blue","green","yellow","red")[z%/%10+1]
image.plot(x, y, z, col = zcol)

However, if you mean:

1 < z <= 10 : blue
...

you would have to do something like:

zcol<-c("blue","green","yellow","red")[(z-0.001)%/%10+1]

Jim

```