将经纬度坐标转换为 R 中的国家/地区名称

我有一个纬度和经度坐标列表，并希望找出它们都居住在哪个国家/地区。

我修改了一个答案这个关于美国各州的问题 https://stackoverflow.com/questions/8751497/latitude-longitude-coordinates-to-state-code-in-r，并且有一个工作函数，但是我遇到了一个问题worldHires地图（来自mapdata包）已经过时了，并且包含许多过时的国家，例如南斯拉夫和苏联。

我如何修改这个函数以使用更现代的包，例如rworldmap？到目前为止我只能让自己感到沮丧......

library(sp)
library(maps)
library(rgeos)
library(maptools)

# The single argument to this function, points, is a data.frame in which:
#   - column 1 contains the longitude in degrees
#   - column 2 contains the latitude in degrees
coords2country = function(points)
{
    # prepare a SpatialPolygons object with one poly per country
    countries = map('worldHires', fill=TRUE, col="transparent", plot=FALSE)
    names = sapply(strsplit(countries$names, ":"), function(x) x[1])

    # clean up polygons that are out of bounds
    filter = countries$x < -180 & !is.na(countries$x)
    countries$x[filter] = -180

    filter = countries$x > 180 & !is.na(countries$x)
    countries$x[filter] = 180

    countriesSP = map2SpatialPolygons(countries, IDs=ids, proj4string=CRS("+proj=longlat +datum=wgs84"))


    # convert our list of points to a SpatialPoints object
    pointsSP = SpatialPoints(points, proj4string=CRS("+proj=longlat +datum=wgs84"))


    # use 'over' to get indices of the Polygons object containing each point 
    indices = over(pointsSP, countriesSP)


    # Return the state names of the Polygons object containing each point
    myNames = sapply(countriesSP@polygons, function(x) x@ID)
    myNames[indices]
}

##
## this works... but it has obsolete countries in it
## 

# set up some points to test
points = data.frame(lon=c(0, 5, 10, 15, 20), lat=c(51.5, 50, 48.5, 47, 44.5))

# plot them on a map
map("worldHires", xlim=c(-10, 30), ylim=c(30, 60))
points(points$lon, points$lat, col="red")

# get a list of country names
coords2country(points)
# returns [1] "UK"         "Belgium"    "Germany"    "Austria"    "Yugoslavia"
# number 5 should probably be in Serbia...

感谢您精心构造的问题。 只需要进行几行更改就可以使用 rworldmap（包含最新的国家/地区），如下所示。我不是 CRS 方面的专家，但我认为我对 proj4string 所做的更改不会产生任何影响。其他人可能想对此发表评论。

这对我有用并给出：

> coords2country(points)
[1] United Kingdom     Belgium            Germany            Austria           
[5] Republic of Serbia

一切顺利， 安迪

library(sp)
library(rworldmap)

# The single argument to this function, points, is a data.frame in which:
#   - column 1 contains the longitude in degrees
#   - column 2 contains the latitude in degrees
coords2country = function(points)
{  
  countriesSP <- getMap(resolution='low')
  #countriesSP <- getMap(resolution='high') #you could use high res map from rworldxtra if you were concerned about detail

  # convert our list of points to a SpatialPoints object

  # pointsSP = SpatialPoints(points, proj4string=CRS(" +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0"))

  #setting CRS directly to that from rworldmap
  pointsSP = SpatialPoints(points, proj4string=CRS(proj4string(countriesSP)))  


  # use 'over' to get indices of the Polygons object containing each point 
  indices = over(pointsSP, countriesSP)

  # return the ADMIN names of each country
  indices$ADMIN  
  #indices$ISO3 # returns the ISO3 code 
  #indices$continent   # returns the continent (6 continent model)
  #indices$REGION   # returns the continent (7 continent model)
}