How to arrange the position of this legend - r

Question

As shown in the map below, how can I place the legend to the last cell in the grid?
The code I used is
psp1 <- tm_shape(province) +
tm_borders(col = 'black') +
tm_shape(county) +
tm_polygons(col = 'estimate', title = 'Changes in %', style = 'fixed', palette = brewer.pal(n = 6, name = 'Spectral'),
breaks = c(-15, -10, -5, 0, 5, 10, 15), legend.hist = F) +
tm_facets('warming', ncol = 2) +
tm_shape(province) +
tm_borders(col = 'black') +
tm_compass(north = 0, type = 'arrow', show.labels =0, position = c('right','top')) +
tm_layout(legend.format = list(fun = function(x) formatC(x, digits = 1, format = "f")),
fontface = 'bold',
legend.text.size = 1.3,
legend.width = 0.2,
legend.title.size = 1.5,
panel.label.size = 1.5,
panel.label.fontface = 'bold')
The data can be found from here. Thanks.

Answer 1

My answer comes perhaps a little late... (almost one year after your request!) Anyway, your question is very interesting and I hope this answer will be useful, either now or for future projects, for you or other SO users (by the way, thanks for having kept your input data accessible for a year ;-)).
As far as I know, it is not possible to solve your problem by using the tm_facets() function of the tmap library. So I suggest a slightly different "strategy" (still using the tmap library) to get what you are looking for.
It is articulated in two steps:
Build the maps and the legend manually... fortunately, not quite manually since the solution I suggest uses one custom function (i.e. make_graph()) that is run through a Map() function.
Edit the map mosaic with the legend using the R base grid library. Again, the implementation is made easier by the use of one custom function (i.e. Maps_setup()) run through a Map() function.
So, please find below a reprex that details the approach.
Reprex
STEP 1 - BUILDING THE MAPS AND THE LEGEND
library(sf)
library(tmap)
library(RColorBrewer)
# Import data
province <- st_read("province.shp")
county <- st_read("county.shp")
# Split the 'sf' object 'county' into a list of five 'sf' objects corresponding
# to the five warming scenarios (i.e. the first five facets of the final figure)
county_warm_list <- split(county , f = county$warming)
# Build the function 'make_graph' to generate the maps
make_graph <- function(x,y){
results <- tm_shape(x,
is.master = TRUE) +
tm_polygons(col = 'estimate',
title = 'Changes in %',
style = 'fixed',
palette = brewer.pal(n = 6, name = 'Spectral'),
breaks = c(-15, -10, -5, 0, 5, 10, 15),
legend.hist = FALSE,
midpoint = 0) +
tm_shape(province) +
tm_borders(col = 'black') +
tm_compass(north = 0,
type = 'arrow',
show.labels = 0,
position = c(0.93, 0.87),
size = 1.2) +
tm_layout(legend.show = FALSE,
# NB: the use of the 'get_asp_ratio()' function enables
# to optimize the size of each map inside its own facet:
asp = tmaptools::get_asp_ratio(x),
panel.labels = y,
panel.label.size = 0.8,
panel.label.fontface = 'bold',
inner.margins = c(0.02, 0.02, 0.02, 0.02))
return(results)
}
# Run the 'make_graph()' function through the list of the five 'sf' objects (i.e.
# 'county_warm_list') to generate the maps with their respective title using
# the 'Map()' function
map_titles <- names(county_warm_list)
Maps_list <- Map(make_graph, county_warm_list, map_titles)
# Build the legend using only the object "county"
Maps_legend <- tm_shape(county) +
tm_polygons(col = 'estimate',
title = 'Changes in %',
style = 'fixed',
palette = brewer.pal(n = 6, name = 'Spectral'),
breaks = c(-15, -10, -5, 0, 5, 10, 15),
legend.hist = FALSE,
midpoint = 0) +
tm_layout(legend.only = TRUE,
legend.position = c("center", "center"),
legend.format = list(fun = function(x) formatC(x, digits = 1, format = "f")),
fontface = 'bold',
legend.text.size = 1.3,
legend.width = 0.2,
legend.title.size = 1.5)
# Add the legend to 'Maps_list'
Maps_list$Legend <- Maps_legend
At the end of this first step, you get a list (i.e. Maps_list) containing 6 elements (i.e. five maps and one legend).
STEP 2 - LAYOUT OF THE MOSAIC OF MAPS WITH THE LEGEND
library(grid)
grid.newpage()
# Build the function 'Maps_setup' to set up the layout
Maps_setup <- function(x,y,z){
pushViewport(viewport(layout = grid.layout(nrow = 3, ncol = 2,
widths = unit(7.32, "cm"),
heights = unit(5, "cm"))))
setup <- print(x, vp = viewport(layout.pos.row = y, layout.pos.col = z))
return(setup)
}
# Run the 'Maps_setup()' function through the six objects of 'Maps_list' (i.e.
# 5 maps + 1 legend) to place the maps and the legend on the page using
# the 'Map()' function
# The 'pos_row' and 'pos_col' vectors are used to indicate where to place the
# maps as the 'Maps_setup()' function works through the list
pos_row <- rep(1:3, each = 2)
pos_col <- rep(1:2, times = 3)
Final_Results <- Map(Maps_setup, Maps_list, pos_row, pos_col)
Created on 2022-01-25 by the reprex package (v2.0.1)