绘制具有国家/地区值的地图作为R中的颜色？

Question

我有以下简单的示例数据,我想在地图上绘制渐变颜色,对应于给定国家/地区的值.

ddf = read.table(text="
country value
USA 10
UK 30
Sweden 50
Japan 70
China 90
Germany 100
France 80
Italy 60
Nepal 40
Nigeria 20
", header=T)

在谷歌搜索,我发现了几个网站.但是,我正在寻找小而清晰的代码,并且最好是快速的(我发现ggplot方法相对较慢).世界地图的分辨率不必高.

我试过以下代码:

library(maptools)
data(wrld_simpl)
plot(wrld_simpl)

具体国家可以如下所示着色:使用[R]地图包 - 在世界地图上的特定国家着色 使用命令:

plot(wrld_simpl, col = c(gray(.80), "red")[grepl("^U", wrld_simpl@data$NAME) + 1])

但是如何以渐变的颜色获得具有上述数据的地图.谢谢你的帮助.

Answer 1

定义"慢".ggplot提供了一种最灵活的方式,可以在几秒钟的时间内在地图上显示数据.

library(RColorBrewer)
library(maptools)
library(ggplot2)

data(wrld_simpl)

ddf = read.table(text="
                 country value
                 'United States' 10
                 'United Kingdom' 30
                 'Sweden' 50
                 'Japan' 70
                 'China' 90
                 'Germany' 100
                 'France' 80
                 'Italy' 60
                 'Nepal' 40
                 'Nigeria' 20", header=TRUE)

# Pascal had a #spiffy solution that is generally faster

plotPascal <- function() {

  pal <- colorRampPalette(brewer.pal(9, 'Reds'))(length(ddf$value))
  pal <- pal[with(ddf, findInterval(value, sort(unique(value))))]

  col <- rep(grey(0.8), length(wrld_simpl@data$NAME))
  col[match(ddf$country, wrld_simpl@data$NAME)] <- pal

  plot(wrld_simpl, col = col)

}

plotme <- function() {

  # align colors to countries

  ddf$brk <- cut(ddf$value, 
                 breaks=c(0, sort(ddf$value)), 
                 labels=as.character(ddf[order(ddf$value),]$country),
                 include.lowest=TRUE)

  # this lets us use the contry name vs 3-letter ISO
  wrld_simpl@data$id <- wrld_simpl@data$NAME

  wrld <- fortify(wrld_simpl, region="id")
  wrld <- subset(wrld, id != "Antarctica") # we don't rly need Antarctica

  gg <- ggplot()

  # setup base map
  gg <- gg + geom_map(data=wrld, map=wrld, aes(map_id=id, x=long, y=lat), fill="white", color="#7f7f7f", size=0.25)

  # add our colored regions
  gg <- gg + geom_map(data=ddf, map=wrld, aes(map_id=country, fill=brk),  color="white", size=0.25)

  # this sets the scale and, hence, the legend
  gg <- gg + scale_fill_manual(values=colorRampPalette(brewer.pal(9, 'Reds'))(length(ddf$value)), 
                               name="Country")

  # this gives us proper coords. mercator proj is default
  gg <- gg + coord_map()
  gg <- gg + labs(x="", y="")
  gg <- gg + theme(plot.background = element_rect(fill = "transparent", colour = NA),
                   panel.border = element_blank(),
                   panel.background = element_rect(fill = "transparent", colour = NA),
                   panel.grid = element_blank(),
                   axis.text = element_blank(),
                   axis.ticks = element_blank(),
                   legend.position = "right")
  gg

}

system.time(plotme())
##  user  system elapsed 
## 1.911   0.005   1.915 

system.time(plotthem())
##  user  system elapsed 
## 1.125   0.014   1.138 

ggplot代码生成以下映射:

每次运行的时间有所不同,但我没有看到它们相隔超过一分钟(我的系统平均接近0.6米,但我不打算进行大量的基准测试).

UPDATE

随着您的要求不断被淘汰,您可以相当容易地用连续的刻度替换离散刻度.

pal <- colorRampPalette(brewer.pal(9, 'Reds'))(length(ddf$value))
palSz <- 10 # not sure what you really want/need for this range

gg <- gg + scale_fill_gradient2(low = pal[1],
                                mid = pal[palSz/2],
                                high = pal[palSz],
                                midpoint = (max(ddf$value) + min(ddf$value)) / 2,
                                name="value")

但是,听起来你可能应该坚持@Andy's,rworldmap因为它抽象了复杂性.

Answer 2

如果你想要更少的代码和更粗糙的分辨率图,你可以使用rworldmap.

library(rworldmap)

#create a map-shaped window
mapDevice('x11')
#join to a coarse resolution map
spdf <- joinCountryData2Map(ddf, joinCode="NAME", nameJoinColumn="country")

mapCountryData(spdf, nameColumnToPlot="value", catMethod="fixedWidth")

可以更改默认分类,颜色和图例,请参阅此RJournal报告.

国家代码而不是名称会更快.