Color ramp with the same colour scale across different plots in R

Question

I need to create a few raster figures, but keeping color ramp scale the same, but I also want the color ramp to be a smooth gradient. Is it possible to keep a big number of colors(~100 to have a smooth color ramp), but at the same time have a reasonable number of breaks, so that it's readable?

library(raster)
library(colorRamps)

r1<- raster(ncol=56, nrow=26)
r1[] <- runif(n=56*26,min=-20,max=15)

r2<- raster(ncol=56, nrow=26)
r2[] <- runif(n=56*26,min=-14,max=68)


brk=seq(-50,70,length.out=100)
col=matlab.like(100)

plot(r1, breaks=brk, col=col)
plot(r2, breaks=brk, col=col)

In this case I have a color ramp I wish, but you can't read the breaks labels

And when I decrease the number of breaks, the color ramp becomes all in one color

brk=seq(-50,70,length.out=6)

Answer 1

You might find this easier with ggplot2. In the code below the key is, for each plot, to set the same color values for low, mid, and high and the same limits in scale_fill_gradient2. That guarantees the same data values are mapped to the same colors in each plot. For example:

library(rasterVis)
library(ggplot2)

# Reproducible rasters
set.seed(4598)
r1<- raster(ncol=56, nrow=26)
r1[] <- runif(n=56*26,min=-20,max=15)

r2<- raster(ncol=56, nrow=26)
r2[] <- runif(n=56*26,min=-14,max=68)

# Get range of data values across the two rasters
rng = range(c(getValues(r1), getValues(r2)))

gplot(r1) + 
  geom_tile(aes(fill=value)) +
  ggtitle("r1") +
  scale_fill_gradient2(low="red", mid="green", high="blue", 
                       midpoint=mean(rng),    # Value that gets the middle color (default is zero)
                       breaks=seq(-100,100,10),  # Set whatever breaks you want
                       limits=c(floor(rng[1]), ceiling(rng[2])))  # Set the same limits for each plot

gplot(r2) + 
  geom_tile(aes(fill=value)) +
  ggtitle("r2") +
  scale_fill_gradient2(low="red", mid="green", high="blue", 
                       midpoint=mean(rng),    # Value that gets the middle color (default is zero)
                       breaks=seq(-100,100,10),  # Set whatever breaks you want
                       limits=c(floor(rng[1]), ceiling(rng[2])))  # Set the same limits for each plot