tmap布局问题：原生布局右侧空白过多与plot_grid组合时图例重叠的解决方案求助

大家好，我正在尝试用tmap搭建一个标准化的地图布局，需求是左侧显示地图，右侧放置图例、可选的简短文本说明以及项目logo，但遇到了两个棘手的布局问题，希望能得到社区的帮助：

问题1：原生tmap布局右侧存在大量多余空白 #

我已经通过tmap的布局参数对齐了所有需要的组件（地图、图例、标题文本、logo、指北针、比例尺），但图例右侧始终有大片空白区域。开启tm_design_mode()后能看到这部分是浅绿色的外部单元格空间，我希望把右侧的所有元素（图例、文本、logo）整体右移，给地图区域分配更多的空间。

对应代码： #

library(tmap)
library(cowplot)
library(grid)
library(png)
library(RCurl)

# 准备数据
countries <- World[World$name=="Germany" | World$name=="Poland",]

# 构建tmap对象
tm_c <- tm_shape(countries) + 
  tm_fill("name", 
          fill.scale=tm_scale(values="rainbow_pu_br"),
          fill.legend = tm_legend(title="countries", 
                                 frame=F, 
                                 text.size=0.5, 
                                 title.size = 0.5, 
                                 position = tm_pos_out(pos.h = 0, pos.v = 0.75))) + 
  tm_compass(type="arrow", position=tm_pos_in("LEFT","TOP"), size=1) + 
  tm_scalebar(breaks=c(0,50,100,200), position=tm_pos_in("RIGHT","BOTTOM")) + 
  tm_title( text=c("data description:\nline a\nline b\nline c\nline d\n \n"), 
           size=0.5, 
           position = tm_pos_out(pos.h = 0, pos.v = 0.9)) + 
  tm_title( text=c("Institute for Mapmaking\nLayout Section"), 
           size=0.3, 
           position=tm_pos_out(pos.h = 0, pos.v = 0.1)) + 
  tm_logo("https://www.r-project.org/logo/Rlogo.png", 
          position = tm_pos_out(pos.h = 0, pos.v = 0.16), 
          height=1) + 
  tm_layout(frame=F, 
            asp=0, 
            legend.outside.size=0.11, 
            outer.margins = c(0,0,0,0), 
            inner.margins = c(0.01,0.01,0.01,0.01))

# 绘图与保存
print(tm_c)
tmap_save( tm=tm_c, filename="tm_c_blank.png", width=15, height=10, units="cm", dpi=300, asp=0, outer.margins = c(0,0,0,0) )

问题截图： #

问题2：用cowplot::plot_grid组合元素时图例与地图重叠 #

为了更灵活地控制布局，我尝试用plot_grid将地图、文本说明、图例、logo拆分成独立组件后再组合，但出现了图例与地图重叠的问题。我希望图例能被放置在指定的浅蓝色矩形区域内，不与左侧的地图产生重叠。

对应代码： #

# 构建各独立组件
map <- grobTree(rectGrob(gp=gpar(col="white")), 
                tmap_grob(tm_shape(countries) + 
                            tm_fill("name", 
                                    fill.scale=tm_scale(values="rainbow_pu_br"),
                                    fill.legend = tm_legend(title="countries", 
                                                           frame=F, 
                                                           text.size=0.5, 
                                                           title.size = 0.5, 
                                                           position = tm_pos_out(pos.h = 0, pos.v = 0.75))) + 
                            tm_compass(type="arrow", position=tm_pos_in("LEFT","TOP"), size=1) + 
                            tm_scalebar(breaks=c(0,50,100,200), position=tm_pos_in("RIGHT","BOTTOM")) + 
                            tm_layout(frame=F, 
                                      asp=0, 
                                      legend.outside.size=0.11, 
                                      outer.margins = c(0,0,0,0), 
                                      inner.margins = c(0.01,0.01,0.01,0.01), 
                                      legend.show=F)) )

header <- grobTree(rectGrob(gp=gpar(fill="orange", col="white")), 
                   textGrob("line1\nline2\nline3\nline4", x=0.15, y=0.5, gp = gpar(col = "black", fontsize = 8)))

r_logo <- readPNG(getURLContent("https://www.r-project.org/logo/Rlogo.png"), FALSE)
credit <- grobTree(rectGrob(gp=gpar(fill="green", col="white")), 
                   rasterGrob(r_logo, x=0.25, y=0.9, width=0.3, just=c("center","top")), 
                   textGrob("Institute of Map making\nLayout Section", x=0.1, y=0.1, just=c("left","bottom"), gp = gpar(col = "black", fontsize = 8)))

leg <- grobTree(rectGrob(gp=gpar(fill="lightblue", col="white")), 
                tmap_grob(tm_c + tm_layout(text.size=0.8, legend.only= T)))

# 组合右侧元素与最终布局
right_side <- plot_grid(header, leg, credit, ncol=1, rel_heights=c(1,2,1))

# 保存最终图
png("tm_c_grid.png", width = 15, height = 10, units="cm", res=300, pointsize=10)
plot_grid(map, right_side, ncol=2, rel_widths=c(3, 1), scale=0.97)
dev.off()

问题截图： #

求助需求 #

我想知道：

1. 如何调整tmap原生布局的参数，消除图例右侧的多余空白，让右侧元素整体右移，给地图更多空间？
2. 如果用cowplot::plot_grid的方式组合组件，需要怎么调整参数才能避免图例与地图重叠，实现紧凑的左图右元素的布局？

感谢大家的帮助！

内容来源于stack exchange