R raster levelplot in multiplot window w/ categorical legend

Question

I am attempting to make a multipanel plot in R that contains a number of different rasters. I am working on a Windows machine.

The rasters are to displayed in the following format:

First row should contain a single raster (centered), with a visible "main" title and ylabel.

Rows 2 through 6 contain two adjacent rasters (ie two columns). The "main" titles are only needed on row 2, as the headings hold for the remaining rows.

Row 7 should contain a categorical legend. Similar to that described in the answer provided here:

https://gis.stackexchange.com/questions/73143/legend-of-a-raster-map-with-categorical-data

The spacing is important. I would like to minimize the distance between rows 2 and 8, while preserving some extra space between row 1 and 2 to allow for the titles. Each raster should be the same size.

Please find a reproducible example of what I'm working on below. I'm unsure why the colored background to the "main" titles are produced, and occurred after I attempted to reduce the white space with the "top.padding" and "bottom.padding" commands.

---

library(raster)

library(rasterVis)

f <- system.file("external/test.grd", package="raster")

r <- raster(f)

rmat = as.matrix(r) 

pc = c(0,0.6,0.8,0.9,0.92,0.95,0.97,0.98,0.99,1) 

digits_n = c(0,1,c(rep(0,length(pc)-2)))

color_breaks = NULL

for (i in 1:length(pc)){color_breaks = c(color_breaks, signif(quantile(c(rmat[which(!is.na(rmat))]),pc[i]), digits = digits_n[i]))}

color_breaks = unique(color_breaks)

color_type = c(colorRampPalette(c("snow1","snow3","seagreen","orange","firebrick"))(length(color_breaks))) 

ss = stack(r)

p0 = levelplot(ss, col.regions=color_type, colorkey=FALSE,margin=FALSE, at=color_breaks,names.attr=c(2000), xlab=NULL, ylab=c("A0"), scales=list(draw=FALSE), par.settings=list(layout.heights=list(bottom.padding=-2)))

ss = stack(r,r)

p1 = levelplot(ss,col.regions=color_type, colorkey=FALSE, margin=FALSE, at=color_breaks, names.attr=c(2050,2100), xlab=NULL, ylab=c("A1"), scales=list(draw=FALSE), layout=c(2,1), par.settings=list(layout.heights=list(top.padding=-2,bottom.padding=-2)))

ss = stack(r,r)

p2 = levelplot(ss,col.regions=color_type, colorkey=FALSE, margin=FALSE, at=color_breaks, names.attr=c("",""), xlab=NULL, ylab=c("A2"), scales=list(draw=FALSE), layout=c(2,1), par.settings=list(layout.heights=list(top.padding=-2,bottom.padding=-2))) 

ss = stack(r,r)

p3 = levelplot(ss,col.regions=color_type, colorkey=FALSE, margin=FALSE, at=color_breaks, names.attr=c("",""), xlab=NULL, ylab=c("A3"), scales=list(draw=FALSE), layout=c(2,1), par.settings=list(layout.heights=list(top.padding=-2,bottom.padding=-2))) 

ss = stack(r,r)

p4 = levelplot(ss,col.regions=color_type, colorkey=FALSE, margin=FALSE, at=color_breaks, names.attr=c("",""), xlab=NULL, ylab=c("A4"), scales=list(draw=FALSE), layout=c(2,1), par.settings=list(layout.heights=list(top.padding=-2,bottom.padding=-2)))

ss = stack(r,r)

p5 = levelplot(ss,col.regions=color_type, colorkey=FALSE, margin=FALSE, at=color_breaks, names.attr=c("",""), xlab=NULL, ylab=c("A5"), scales=list(draw=FALSE), layout=c(2,1), par.settings=list(layout.heights=list(top.padding=-2,bottom.padding=-2))) 

windows()

print(p0, split= c(1,1,1,7), between = c(3,3))

print(p1, split= c(1,2,1,7), newpage=FALSE)

print(p2, split= c(1,3,1,7), newpage=FALSE)

print(p3, split= c(1,4,1,7), newpage=FALSE)

print(p4, split= c(1,5,1,7), newpage=FALSE)

print(p5, split= c(1,6,1,7), newpage=FALSE)

---

I would then like to add in the legend in row 7 with something similar to the following:

legend("center", 
    ncol = length(color_breaks)/2,
    legend=c(color_breaks),
    fill=color_type,cex=0.6, 
    title=expression(bold("Magnitude [ UNITS ]")), box.col = FALSE, xjust = 0, title.adj = 0
    )

I would post the image I obtain but I guess I need reputation points.

Why has the background color in the titles appeared? How can I reduce the spacing between rows 2 and 6 while increasing the space between row 1 and 2? How to now add in the categorical legend in row 7?

Thank you.

Answer 1

I will try to answer briefly your questions:

1. The background color of the strip regions is the default value in lattice . The rasterTheme sets it to white but you have to use par.settings instead of col.regions as described here .
2. You should try the panel.width and panel.height arguments of print.trellis .
3. levelplot is able to plot categorical rasters with an appropriate legend, but you have to define the raster accordingly. Here you will find an example.