tmap：删除 legend.outside 右侧的空白

Question

I got this plot

using this script

library(raster)
library(tmap)
library(classInt)

download.file("https://github.com/mtennekes/tmap/files/5500015/Difference.tif.zip",
              "Difference.tif.zip")

unzip("Difference.tif.zip", "Difference.tif")

diff <- raster("Difference.tif")

diff_values <- getValues(diff)

diff_values_below0 <- diff_values[diff_values < 0]
diff_values_above0 <- diff_values[diff_values > 0]

classes1 <- classIntervals(diff_values_below0, n = 4, style = "fisher")
classes2 <- classIntervals(diff_values_above0, n = 4, style = "fisher")

all_classes <- c(classes1$brks, classes2$brks)


diff_map<- 
  tm_shape(diff) + 
  tm_raster(midpoint = 0, 
            breaks = all_classes,
            palette = "RdBu")+
  tm_layout(legend.outside = TRUE)

tmap_save(diff_map, "diff_map.png", width=1000, height=700,dpi = 150)

As you can see, there is white space to the right of the legend. I tried removing it using outer.margins but none of my trials worked.

Any suggestions on how this can be done?

Answer 1

My compliments to you for writing a well documented question. The general strategy for modding graphics in R is to first identify which of the three plotting paradigms are in play and then make a new function that is but a minor modification of the code. A more specific strategy is to carefully read the documentation and then make mods to your parameters. I chose a middle ground because I assumed you'd already done the second one.

Looking at the code for tm_layout it appeared to be mostly substitutions of graphics parameters for base graphics, but that was just a guess. I then took a further guess that legend.width was the parameter to modify (I chose as a starting point, 0.2) but I got the warning message:

Warning message: In preprocess_gt(x, interactive = interactive, orig_crs = gm$shape.orig_crs): legend.width controls the width of the legend within a map. Please use legend.outside.size to control the width of the outside legend

Then looking at the result in my file browser I saw.... no improvement. So heeding the warning I tried again, this time altering the legend.outside.size parameter. It did move the plot location over to the right but I was getting a different warning with that parameter set to 0.15:

Legend labels were too wide. The labels have been resized to 0.54, 0.59, 0.59, 0.59, 0.62, 0.66, 0.66, 0.60, 0.55. Increase legend.width (argument of tm_layout) to make the legend wider and therefore the labels larger. Map saved to /home/david/Downloads/diff_map3.png Resolution: 1000 by 700 pixels Size: 6.666667 by 4.666667 inches (150 dpi)

See if the result is more to your liking. (t does not appear to me that the legend labels are too wide.