地图中一组特定国家的边界​​线

Question

我正在绘制如下欧洲地图：

library(ggplot2)
library(grid)
library(rworldmap)

## Get the world map: ##
worldMap <- getMap()

## Define vector with all European countries: ##
v.europe <- c("Norway", "Sweden", "Finland", "Denmark", "United Kingdom","Ireland", "Greece",
              "Belgium", "Netherlands", "France", "Spain", "Portugal", "Luxembourg", "Croatia",
              "Germany", "Switzerland", "Austria", "Slovenia", "Italy", "Bulgaria", "Romania",
              "Czech Rep.", "Slovakia", "Hungary", "Poland", "Bosnia Hercegovina", "Serbia",
              "Turkey", "Ukraine", "Moldova", "Belarus", "Estonia", "Latvia", "Lithuania",
              "Montenegro", "Albania", "Macedonia")

## Select only the index of countries of Europe: ##
indEU <- which(worldMap$NAME%in%v.europe)


## Extract longitude and latitude border's coordinates of countries: ##
df.europeCoords <- lapply(indEU, function(i){
  df <- data.frame(worldMap@polygons[[i]]@Polygons[[1]]@coords)
  df$region = as.character(worldMap$NAME[i])
  colnames(df) <- list("long", "lat", "region")
  return(df)
})
df.europeCoords <- do.call("rbind", df.europeCoords)
names(df.europeCoords) <- c("longitude", "latitude", "country")

## Deletes/Removes borders of PLOT: ##
ax <- list(
  title = "",
  zeroline = FALSE,
  showline = FALSE,
  showticklabels = FALSE,
  showgrid = FALSE
)

## Plot the map: ##
p <- ggplot(data = df.europeCoords, aes(x = longitude, y = latitude, group = country, 
                                        text = paste("<b>", country, '</b>\n')), 
            color = "grey50", size = 0.1) + 
     geom_polygon() +
     coord_map(xlim = c(-13, 35),  ylim = c(32, 71)) +
     theme_classic() +
     theme(axis.text.x = element_blank(), axis.text.y = element_blank(), axis.ticks.x = element_blank(),
           axis.ticks.y = element_blank(), axis.title = element_blank(), legend.position = "none",
           plot.margin = unit(0 * c(-1.5, -1.5, -1.5, -1.5), "lines"))

## Create plot_ly() object: ##
EuropePlot <- plotly::ggplotly(p, tooltip = "text") %>%
              layout(xaxis = ax, yaxis = ax)

这给出了以下情节：

我想在一组国家周围画一个红色边框。该组应包括以下国家：奥地利、德国、丹麦、比利时、法国和瑞士。我该怎么做？

Answer 1

也可以在一组国家周围绘制红色边框。这可以通过使用 sf::st_union() 轻松实现。

在某些国家/地区周围创建带有红色边框的绘图：

  library(tidyverse)
  library(spatialrisk)
  library(sf)  

  red_borders <- spatialrisk::europe_countries %>%
    filter(admin %in% c("Austria", "Germany", "Denmark", 
                        "Belgium", "France", "Switzerland"))

  ggplot() +
    geom_sf(data = spatialrisk::europe_countries) +
    geom_sf(data = red_borders, color = "red") +
    theme_void()

或者删除 sf-object 中的内部边界：

  ggplot() +
    geom_sf(data = spatialrisk::europe_countries) +
    geom_sf(data = sf::st_union(red_borders), color = "red", alpha = 0) +
    theme_void()

^{由reprex package (v0.3.0) 于 2020 年 10 月 11 日创建}

Answer 2

也许最简单的方法是在您的数据框中创建一个新列，作为应将哪些国家/地区标记为红色的标志：

df.europeCoords$red <- df.europeCoords$country %in% 
  c("Austria", "Germany", "Denmark", "Belgium", "France", "Switzerland")

现在您将此变量映射到颜色美学，在red 列中为FALSE 的国家指定轮廓颜色NA，为具有TRUE 值的国家指定"red"：

p <- ggplot(data = df.europeCoords, 
            aes(x = longitude, y = latitude, group = country, 
                text = paste("<b>", country, '</b>\n')),
            color = "grey50", size = 0.1) + 
     geom_polygon(aes(color = red), size = 1) +
     scale_color_manual(values = c(NA, "red")) +
     coord_map(xlim = c(-13, 35),  ylim = c(32, 71)) +
     theme_classic() +
     theme(axis.text.x  = element_blank(), 
           axis.text.y  = element_blank(), 
           axis.ticks.x = element_blank(),
           axis.ticks.y = element_blank(), 
           axis.title   = element_blank(), 
           legend.position = "none",
           plot.margin = unit(0 * c(-1.5, -1.5, -1.5, -1.5), "lines"))

p