Arrange odd number of plots using rasterVis and gridExtra

I am trying to plot a panel with seven rasters using the levelplot function of the rasterVis package, combined with gridExtra 's grid.arrange .

I almost get what I need by using the following code:

# load required packages
library(rasterVis)
library(gridExtra)

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

# create plots
p1 <- levelplot(r, xlab=NULL, ylab=NULL, margin=FALSE)
p2 <- levelplot(r*2, xlab=NULL, ylab=NULL, margin=FALSE,colorkey=FALSE)

# put plots in list
p.list <- list(p1,p2,p2,p2,p2,p2,p2)

# create layout
lay <- rbind(c(1,1,1),
             c(2,3,4),
             c(5,6,7))

# arrange plots
grid.arrange(grobs=p.list, layout_matrix=lay)

which yields this figure:

However, there are some things I still need to improve:

How to decrease the blank space between the plots in the bottom rows?

How to add a single, combined legend for the six bottom rasters, preferentially put to the bottom of the figure?

Is this possible to achieve using rasterVis and gridExtra ? Is there any other approach that can be used?

---

The white space is a combination of lattice margin settings, but also the plots having a fixed aspect ratio (they can't be too close unless the device itself has a compatible aspect ratio).

With regards the legend, you could use draw.colorkey() , but from what I can tell you need to manually ensure that the colours match by passing them explicitly to both plots and the key.

# load required packages
library(rasterVis)
library(gridExtra)

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

my_theme <- rasterTheme(region = blues9)

# create plots
p1 <- levelplot(r, xlab=NULL, ylab=NULL, margin=FALSE, par.settings = my_theme)
leg <- p1$legend$right$args$key
p1$legend <- list()
p2 <- levelplot(r*2, xlab=NULL, ylab=NULL, margin=FALSE,colorkey=FALSE, par.settings = my_theme)

# put plots in list
p.list <- list(p1,p2,p2,p2,p2,p2,p2)

# create layout
lay <- rbind(c(NA,1,NA),
             c(2,3,4),
             c(5,6,7),
             c(8,8,8))

leg$col <- my_theme$regions$col
legGrob <- draw.colorkey(key = leg, vp = grid::viewport(height=0.5))
# arrange plots
grid.arrange(grobs=c(p.list, list(legGrob)), layout_matrix=lay,
             vp = grid::viewport(width=0.7,height=1))

(needless to say, facetting seems the better option by a wide margin)

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