使用地图包为 r 中的部分国家创建全球等值线图

Question

我有一个包含两列的数据框，例如下面的

df

，我想使用

maps::map()

来创建一个全局等值线图。我希望将颜色分配给

df

中存在的那些国家，剩下的只是空的无色多边形。但是结果和我预想的大相径庭。我尝试使用以下脚本： 另外，为什么世界地图质量这么低？有没有办法让它变得更好？

df <- tribble(
  ~Country, ~Value,
  "Jordan", 35,
  "USA", 84,
  "Turkey", 65,
  "Pakistan", 43
)

percent_map <- function(var, color, legend.title, min = 0, max = 100) {
  
  # generate vector of fill colors for map
  shades <- colorRampPalette(c("white", color))(100)
  
  # constrain gradient to percents that occur between min and max
  var <- pmax(var, min)
  var <- pmin(var, max)
  percents <- as.integer(cut(var, 100, 
                             include.lowest = TRUE, ordered = TRUE))
  fills <- shades[percents]
  
  # plot choropleth map
  maps::map("world", fill = TRUE, col = fills, 
            resolution = 0,
            myborder = 0, mar = c(0,0,0,0))
  
  # overlay state borders
  maps::map("world", col = "white", fill = FALSE, add = TRUE,
            lty = 1, lwd = 1, 
            myborder = 0, mar = c(0,0,0,0))
}

percent_map(var = df$Value, 
            color = "darkgreen", 
            legend.title = "Global Map for Value", 
            min = 0, max = 100 
)