如何使用 maptools、ggplot 或其他包在 R 中的地图中添加城市和质心的名称？

问题描述

我正在尝试将带有标签和点的省份和城市的标签合并到南非地图中。我可以从网站 https://gadm.org/download_country_v3.html

的 spdf 文件中获取带有省级细分的地图

SA1spdf <- readRDS("gadm36_ZAF_1_sp.rds")

我正在尝试使用插槽中的信息：

SA1spdf@data@ADM1_EN

包含9个省的标签 如果可能的话，我想将标签放在多边形的中心，所以我得到了 9 个省的质心：

centroids_SAdf <- as.data.frame(coordinates(SA1spdf))    

并将名称 V1 和 V2 更改为经度和纬度

names(centroids_SAdf) <- c("Longitude","Latitude")

我还想在图中添加一些城市：

coordinates_cities <- data.frame(city = c("Cape Town","Durban","Johannesburg","Port Elizabeth"),lat = c(-33.930,-29.870,-26.190,-33.960 ),lon = c(18.460,30.990,28.040,25.590 )        

但我无法将所有这些链接在一起。

我可以通过以下方式获取地图：

qtm(SA1spdf,fill = "white")       

使用maptools和以下代码都返回错误信息

qtm(SA1spdf,fill = "white") + tm_text("SA1spdf$data#ADMN1_EN")    

tm_shape(SA1spdf) + tm_polygons() + tm_fill(col = "white")    

我没有得到一张白色填充的地图，它是灰色的

以下代码返回错误消息：

tm_shape(SA1spdf) + tm_polygons() + tm_text(c("Eastern Cape","Free State","Gauteng","KwaZulu-Natal","Limpopo","mpumalanga","north West","Nothern Cape","Western Cape"))    

ggplot(SA1spdf,aes(x = lon,y = lat),group = group) + geom_polygon(fill = "white") + geom_point(data = coordinates_cities,aes(x = lat,y = lon)) + geom_text(data= coordinate_cities,aes(label = city))    

解决方法

library(sp)
library(ggplot2)
library(tmap)
library(rgeos)

我将使用您使用 ZAF 中的数据创建的同一对象 SA1spdf 作为 GADM 中的 sp 对象

coordinate_cities <- data.frame(
  city = c("Cape Town","Durban","Johannesburg","Port Elizabeth"),lat = c(-33.930,-29.870,-26.190,-33.960),long = c(18.460,30.990,28.040,25.590))        

基础图

plot(SA1spdf)
points(coordinate_cities$lon,coordinate_cities$lat,pch = 16,col = "red",cex = 1)
text(coordinate_cities$lon,coordinate_cities$city,adj = c(0,0),cex = 0.7)
title(main = "South Africa",sub = "Main cities")

ggplot2

sa_df <- fortify(SA1spdf)
#> Regions defined for each Polygons

ggplot(sa_df,aes(long,lat)) +
geom_polygon(aes(group = group),fill = "white",colour = "black") +
geom_point(data = coordinate_cities,aes(x = long,y = lat),colour = "red") +
geom_text(data = coordinate_cities,aes(label = city),vjust = -1) +
coord_equal()

tmap

# convert coordinate_cities to sp object
sa_cities_spdf <- SpatialPointsDataFrame(coords = coordinate_cities[,c("long","lat")],data = coordinate_cities[,"city",drop = FALSE],proj4string = CRS("+proj=longlat +datum=WGS84"))

tm_shape(SA1spdf) +
  tm_borders() +
  tm_layout(main.title = "South Africa regions") +
  tm_text("NAME_1",size = 0.7) +
  tm_shape(sa_cities_spdf) + tm_symbols(size = 0.5,col = "red")

^{由 reprex package (v0.3.0) 于 2021 年 6 月 17 日创建}