r - geom_polygon 填充中的纹理

Question

我需要创建一张欧洲 map 来显示某个变量在各个国家/地区的分布情况。我需要黑白 map 。我依靠 ggplot 并遵循了这个 approach举个例子。我根据 this blogpost 更改了图例.所有这一切都适用于这个结果:

我的问题是如何更改 map ，使我缺少填充信息并显示为纯白色的国家/地区上面有纹理(我想是对角线)？

由于我的脚本有点乱，这里只展示ggplot，没有数据准备部分:

require(ggplot2)

plotCoords <- read.csv("http://eborbath.github.io/stackoverflow/PlotCoords.csv")
showCoords <- read.csv("http://eborbath.github.io/stackoverflow/showCoords.csv")


ggplot() +
  geom_polygon(
    data = plotCoords,
    aes(x = long, y = lat, group = group),
    fill = "white", colour = "darkgrey", size = 0.6) +
  geom_polygon(
    data = showCoords,
    aes(x = long, y = lat, group = group),
    fill = "grey", colour = "black", size = 0.6) +
  geom_polygon(
    data = showCoords,
    aes(x = long, y = lat, group = group, fill = sh_left),
    colour = "black", size = 0.1) +
  scale_fill_gradient(
    low = "gray90", high = "gray0",
    name = "Share of left-wing protesters",
    guide = guide_colorbar(
      direction = "horizontal",
      barheight = unit(2, units = "mm"),
      barwidth = unit(50, units = "mm"),
      draw.ulim = F,
      title.position = 'top',
      title.hjust = 0.5,
      label.hjust = 0.5
    )) +
  scale_x_continuous(element_blank(), breaks = NULL) +
  scale_y_continuous(element_blank(), breaks = NULL) +
  coord_map(xlim = c(-26, 47),  ylim = c(32.5, 73)) + 
  theme_bw() +
  theme(legend.justification = c(-0.4, 1.2), legend.position = c(0, 1))

第一个 geom_polygon 用于背景，我想我必须在那里编辑 fill。显然，这对于区分无信息与变量 I 绘图的低值很重要。考虑到我必须依赖黑白，我想到了使用纹理的想法，但我愿意接受其他建议。

谢谢!

Answer 1

是 technically possible with gridSVG ，但不确定是否值得付出努力。

我在GeomPolygon的基础上新建了geom，修改了draw_panel方法返回，

gl <- by(munched, munched$group, 
         function(m){
           g <- polygonGrob(m$x, m$y, default.units = "native")

           patternFillGrob(g, 
                           pattern = pattern(linesGrob(gp=gpar(col="red",lwd=3)),
                                             width = unit(2, "mm"), height = unit(2, "mm"),
                                             dev.width = 1, dev.height = 1))
         }, simplify = FALSE)

gTree(children = do.call(gList, gl))